- Email: [email protected]
Comedone formation: Etiology, clinical presentation, and treatment
Comedone Formation: Etiology, Clinical Presentation, and Treatment WILLIAM J. CUNLIFFE, MD D. B. HOLLAND A. JEREMY Abstract: An important feature in the etiology of acne is the presence of pilosebaceous ductal hypercornification, which can be seen histologically as microcomedones (Fig 1) and clinically as blackheads, whiteheads, and other forms of comedones, such as macrocomedones. There is a significant correlation between the severity of acne and the number and size of microcomedones (follicular casts), the presence of which is a measure of comedogenesis.1 This correlation can be demonstrated by skin surface biopsy using cyanoacrylate gel. In this procedure, microcomedones are sampled by applying cyanoacrylate gel to the skin surface. A glass microscopic slide is then applied on top of the gel and pressed firmly onto the skin for 1 minute.1–3 The glass slide is gently removed, taking with it the upper part of the stratum corneum and microcomedones, which are then analyzed by low-power microscopy or digital image analysis.1–3
Etiologic Aspects of Comedogenesis
Reasons for Ductal Hyperproliferation
C
Several factors have been implicated in the induction of ductal keratinocyte hyperproliferation, including abnormalities in sebaceous lipid composition, androgens, local cytokine production, and bacteria.
From the Skin Research Centre, University of Leeds, Leeds, UK. Address correspondence to Dr. William J. Cunliffe, General Infirmary at Leeds, Department of Dermatology, Great George Street, Leeds LS1 3EX, UK. E-mail address: [email protected]
Abnormalities in Sebaceous Lipids Sebaceous lipids are unique to humans and are very complex. They consist predominantly of squalene, wax esters, and triglycerides, which, when metabolized by cutaneous bacterial lipases, produce a complex array of free fatty acids. Of the abnormal sebaceous lipids in acne patients, linoleate levels may be relevant. Examination of polar lipids recovered from comedones shows that the acyl ceramides contain only 6% linoleate among the esterified fatty acids, compared with 45% in normal human epidermis.9 –11 Linoleic acid is reduced in sebum from acne subjects, but returns to normal with resolution of acne after treatment with oral isotretinoin and oral antiandrogens.12 A low level of linoleate also results in a decreased epidermal barrier function, which might render the comedonal wall permeable to inflammatory substances. Membrane-coated granules13–15 are probably more related to barrier permeability than to cell separation and are decreased in comedones, but the significance of this finding remains unclear. Other lipids have been incriminated in comedone formation; in particular, an increase in other free fatty acids and squalene have been blamed for inducing comedones.14,16,17 This has been demonstrated in the rabbit-ear model;18 however, the development of a human model for comedogenesis has suggested that the rabbit model may be inappropriately overreactive.19
omedones result from abnormalities in the proliferation and differentiation of ductal keratinocytes. Comedones represent the retention of hyperproliferating ductal keratinocytes/corneocytes in the duct. This hyperproliferation has been confirmed by demonstration of an increase in 3H-thymidine labeling of comedones4 and an increase in the Ki-67 labeling of ductal keratinocytes.5 This technique has also demonstrated an increase in the proliferation of ductal keratinocytes of “nonaffected” follicles, which were biopsied as clinically “normal” follicles from an area affected by acne.5 This fits with the histological observation of microcomedones being found in 30% of (serially sectioned) tissue sections of clinically “normal” skin taken from around acne lesions. Further evidence of ductal hyperproliferation is the presence of keratins 6 and 16 (keratin markers of hyperproliferation) in microcomedones and comedones.6 The primary abnormality that gives rise to hypercornification is not related to changes in keratin expression.7 Comedogenesis could also be due to the failure of ductal keratinocytes to adequately separate. Studies of involucrin expression and desmosomes, which are features of terminal differentiation, have shown no difference between follicles from acne and control biopsy specimens.8 More research is required on this important issue of ductal corneocyte adhesion.
© 2004 by Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010
0738-081X/04/$–see front matter doi:10.1016/j.clindermatol.2004.03.011
368 CUNLIFFE ET AL.
Clinics in Dermatology
Y
2004;22:367–374
Figure 1. A microcomedone.
Laboratory animals do not develop whiteheads or inflamed acne lesions, even though the rabbit ear readily produces comedones.17 The rhino mouse is an alternative useful model for comedogenesis.20,21 It is important emphasize that neither of these animal models demonstrated inflammation, which frequently occurs in humans. Androgen Control of Comedogenesis Evidence is now accumulating suggesting that androgens may play an important role in comedogenesis. There is a correlation between comedone numbers in early acne and DHEAS levels in prepubertal individuals.22 Comedones are frequently seen before puberty and often precede the development of inflammation by several months or even 1–2 years (Fig 2). Cells of the pilosebaceous duct have androgen receptors,23 and 5␣reductase type I is also present in these cells in both health and disease.24 –26 Antiandrogen-containing drugs, such as cyproterone acetate in the drug co-cyprindiol (Dianette, Estelle 35), reduce comedones. Co-
Figure 2. This prepubertal female exhibits inflammatory lesions. These were preceded for 2 years by blackheads.
Figure 3. A normal pilosebaceous duct grown in vitro. (With permission from Dr. Terence Kealey).
cyprindiol also increases sebaceous linoleate concentration,12 and thus antiandrogen therapy could modulate comedogenesis both directly and indirectly by influencing sebaceous lipids. Cytokines and Comedone Formation Cytokine production by ductal keratinocytes is also likely important in the formation of comedones. Kealey et al27–29 developed an excellent in vitro model for growing the duct. Interleukin (IL)-1␣ is present in many comedones at levels likely to be biologically and pathologically relevant30 and induces comedogenesis (Figs 3 and 4). Furthermore, epidermal growth factor markedly disrupts the duct comedo in vitro.27–32 Kealey et al have provided data to show that the isolated, cultured duct is also a good model for studying the effects of inflammatory cytokines in the etiology of acne. For example, they have shown that epidermal growth factor and transforming growth factor alpha not only affect the pilose-
Clinics in Dermatology
Y
2004;22:367–374
COMEDONE FORMATION
369
Figure 5. This addition of epidermal growth factor in vitro destroys the duct. (With permission from Dr. Terence Kealey.)
opment of comedones. However, bacteria, particularly Propionibacterium acnes, are likely involved later in comedogenesis. Figure 4. This demonstrates that the addition of interleukin-1 alpha can in vitro produce individual a comedone. (With permission from Dr. Terence Kealey.)
baceous duct, but also inhibit sebum production in vitro (Fig 5). 29 Bacteria in Comedogenesis Bacteria are probably not involved in the initiation of comedones. Electron microscopy of early noninflamed lesions taken from prepubertal and early pubertal individuals has demonstrated few or no bacteria.33 Quantification of bacteria from comedones suggests that follicular colonization may be unrelated to comedogenesis.34 Biopsy and culture of early noninflamed lesions has shown that 30% of these are without bacteria,34 suggesting that ductal bacteria are not needed for the initiation of cornification in the devel-
Cycling of Comedones Comedones are temporary structures. This is self- evident to the clinician; otherwise a patient who develops acne at age 11 years and has predominantly comedonal lesions would by late adolescence have a face completely full of such lesions. Clinically this does not happen. Using markers of cell cycling and keratinocyte proliferation, it has been shown that, like the hair follicles, normal pilosebaceous follicles and comedones undergo cyclical growth.35 This cycling phenomenal extends over a period of days or a few weeks rather than, as in the hair follicle, months. Clinical observation on the life cycle of whiteheads show that many whiteheads have resolved within 12 days (Fig 6). Further evidence for the renewal of comedones is that extracted blackheads refill over 2– 6 weeks.
370 CUNLIFFE ET AL.
Figure 6. The lifespan of whiteheads.
Measurements of sebum outflow have demonstrated that functionally some comedones are blocked relatively permanently.36 Others can become blocked temporarily after skin hydration,37 and this obstruction is associated with a decrease in sebum outflow. This observation may explain the precipitation or exacerbation of acne by heat and humidity seen in individuals who work in kitchens and who have traveled in hot, humid environments, such as Majorca, Greece, and the Far East. Certain external chemicals may contribute to comedogenesis. These substances include the ingredients of some cosmetics, such as isopropyl myristate, propylene glycol, and red dyes D and C. Certain drugs applied topically, such as corticosteroids, will also induce comedones, as will other external chemicals, such as chloracnegic agents. Just how such external agents trigger comedogenesis is not adequately understood.
Could Comedone Formation Be Primarily an Inflammatory Process? Recently it has been demonstrated that a significant number of biopsy specimens from the normal-looking
Figure 7. Sandpaper acne; note the presence of many small confluent whiteheads.
Clinics in Dermatology
Y
2004;22:367–374
Figure 8. Extensive macrocomedones.
skin of acne patients that show no evidence of microcomedones or ductal hyperproliferation whatsoever have a significant inflammatory cell infiltrate around the follicle (particularly CD3⫹ and CD4⫹ cells and macrophages).38 For many years dermatologists have been aware, based on data from clinical trials and their own clinical perception, that antimicrobial agents significantly reduce comedonal lesions. This observation by Jeremy et al38 adequately explains this clinical observation, because these inflammatory cells are significantly suppressed by antimicrobial therapy. Thus this explains why such therapies significantly reduce comedones.
The Pilosebaceous Duct Is Not a Hollow Tube Some physicians consider the pilosebaceous duct to be similar to the sweat gland duct in terms of the internal lumenal structure. This is not the case, however. Rather, the pilosebaceous duct is a morass of multiple, intertwining canaliculi, not all of which are connected to the external skin surface. The canaliculi are composed of desquamating corneocytes and sebaceous secretions.
Figure 9. Very large macrocomedones behind the ear.
Clinics in Dermatology
Y
2004;22:367–374
The canaliculi contain are even more degenerated corneocytes, sebum, and bacteria.
Clinical Presentation of Comedones Comedone Types The clinical type of comedo should influence the choice of treatment. It is important that the physician recognize the different types of comedonal lesions and treat them appropriately.39 In most patients, several types of comedones coexist. Microcomedones Microcomedones are histological observations. They can be detected on skin surface biopsy, and their numbers correlate with acne severity.1–3 Serially cut biopsy sections of normal-looking skin in an acne-prone individual will frequently (28%) demonstrate histological features of microcomedones.39 Evaluation of biopsy specimens of papules obtained up to 72 hours after development will reveal a microcomedone in 52% of subjects, a whitehead in 22%, and a blackhead in 10%.40 This finding clearly confirms the practical need to apply topical therapies to apparently noninvolved skin as well as to active acne lesions. Ordinary Comedones Dermatologists recognize the typical pattern of commonly seen comedones (blackheads and whiteheads), and this requires little additional explanation except to stress that whiteheads are usually present in much greater numbers than blackheads. A good light is needed to adequately assess just how many whiteheads most acne patients have. Whiteheads are an essential feature of the clinical picture and thus play a vital role in the development of inflammation. They must be optimally treated; the first choice should be a topical retinoid. Missed Comedones Physicians frequently underestimate the number of comedones. In all patients, it is essential to stretch the skin, using a good light, at a shallow angle; otherwise some comedones may go unrecognized. In about 30% of patients, stretching the skin will reveal comedones that otherwise cannot be seen, thus allowing the prescription of appropriate topical therapy (a topical retinoid). The treatment protocols for ordinary, “missed,” and microcomedones are similar. The topical treatment must be applied not just to the lesions, but also to the adjacent subclinical “normal” skin. Physical methods of therapy, such as blackhead removers, are worthy of consideration in those patients with obvious blackheads, especially if present over a firm, bony surface. Data from numerous clinical trials, some of which are reported elsewhere in this issue, indicate that topical retinoids reduce comedones by 60% after 3 months of therapy. Topical retinoids are an essential part of
COMEDONE FORMATION
371
topical therapy for most acne patients. Topical azaleic acid and salicylic acid also have anticomedonal effects; these agents, as well as topical retinoids, are described in detail in other articles in this issue. The potential for benzoyl peroxide to reduce comedones is often questioned. However, data from clinical trials clearly show that benzoyl peroxide reduces comedones as well as topical retinoids. With topical antibiotics, the reduction in comedones after 3 months of treatment is on the order of 30 – 40%. One of the earliest features in comedone formation is a significant lymphocyte infiltrate around the follicle occurring before any clinical or microscopic evidence of comedones is apparent.38 Antimicrobial therapy for acne also has a direct anti-inflammatory activity against the type of lymphocyte infiltrate present in the precomedonal lesions so described.38 This may explain why antimicrobial therapy reduces comedones. Sandpaper Comedones These predominantly small, closed comedones are almost confluent, giving the skin a “sandpaper” feel (Fig 7). 39 They occur predominately on the forhead and cheek, and often develop into small, inflamed lesions.39 Sandpaper comedones are difficult to treat; on the whole, they show little or variable response to oral antibiotics and topical retinoids. The optimum treatment is oral isotretinoin at a preferred dosage of .5 mg/kg⫺1/daily. Macrocomedones This term refers to blackheads and whiteheads that are ⬎1 mm in size (Fig 8). Macrocomedones occur much more frequently as whiteheads than blackheads. They need to be treated for two reasons. They are a cosmetic problem and may flare into inflamed lesions, particularly in patients treated with oral isotretinoin. In such patients, they are a significant reason for a severe flare of the acne. Macrocomedones are easily missed unless adequate lighting is used and the skin is stretched. The optimum therapy is gentle cautery.41– 43 This is performed under topical local anesthesia using an anesthetic cream such as EMLA, which is applied for 60 –75 minutes under an occlusive dressing such as Tegaderm. The area is then lightly touched with a small hot-wire cautery probe, with the tip gray in color rather than vividly red-hot. The temperature of the cautery should be just high enough to char a paper towel. The purpose is not to significantly burn the skin, but rather to produce low-grade localized thermal damage from the influx of polymorphonucleocytes. This therapy is far superior to topical retinoids; 2 weeks of treatment using light cautery typically produces virtually 100% clearance, In comparison, topical retinoid therapy typically produces ⬍10% reduction (Figs 9 and 10).42 Not all patients respond perfectly; 40% develop recurrent lesions necessitating multiple treatments with
372 CUNLIFFE ET AL.
Clinics in Dermatology
Y
2004;22:367–374
Figure 11. Pomade acne. Note the presence of many whiteheads
depending on how many submarine comedones are present. The comedones are surprisingly quite large, possibly as large as 1 cm. Treatment is difficult; the optimum therapy is probably the gentle cautery de-
Figure 10. The same patient after two sessions of treatment with gentle cautery.
gentle cautery. If the patient is receiving oral isotretinoin and the acne has flared as a consequence of the macrocomedones, then it is necessary to either stop the oral isotretinoin temporarily or reduce the dosage by about 50% until the physical therapy is completed. In such circumstances, a short course of oral corticosteroids (eg, .5 mg/kg daily for 2–3 weeks) may be needed. In all patients treated with gentle cautery, a test area is always treated initially, and thereafter the remaining lesions are treated in further sessions at 2- to 3-week intervals. Scarring and pigment changes are uncommon. Macrocomedones are also a cause of a slow and poor response to oral isotretinoin therapy.44 Submarine Comedones These uncommon types of comedones are easily missed. It is often necessary to stretch the skin to make the correct diagnosis. They usually present as a focus of repeated inflammation at the same site. The inflammation is usually in the form of a nodule or nodules,
Figure 12. Numerous blackheads typical of chloracne.
Clinics in Dermatology
Y
2004;22:367–374
scribed previously for treating macrocomedones. In such patients, the surface of the submarine comedone is gently touched with the cautery at 10 –12 sites over the surface of the large comedone. This procedure stimulates a polymorphonucleocyte response and so allows subsequent drainage of retained corneocytes from the comedone. This technique is successful in about 50% of submarine comedones. The correct Drug-Induced Comedones and Pomade Comedones Drug-induced comedones may result from oral, topical, intranasal, or interthecal corticosteroids44,45 or oral anabolic steroids.46,47 “Blue comedones” can result, albeit very infrequently, from the development of minocycline-induced pigmentation in noninflamed lesions. This condition can be confused with osteoma cutis. Pomade acne occurs especially in Afro-Caribbeans, who apply certain defrizzing agents to their hair (Fig 11). Treatment of drug-induced comedones and pomade acne involves removing the cause and treating with either topical retinoids or gentle cautery. Chloracne Chloracne is also characterized by many persistent comedones.48 –51 Indeed, comedonal acne is a hallmark of this type, and inflammatory lesions are less frequent (Fig 12). In extensive chloracne, scarring may arise even from noninflammatory lesions. Inflamed lesions may be treated with oral antibiotics, topical benzoyl peroxide, or topical antibiotics. Gentle cautery is relatively successful, but there is usually a poor response to topical and oral retinoids.51 The poor response to oral isotretinoin relates to the fact that chloracne is associated with atrophy of the sebaceous gland, and oral isotretinoin primarily helps acne by dramatically reducing the size and function of the gland. Unfortunately, some patients with chloracne have systemic problems, and the disease may persist for many years despite withdrawal of the chloracne agent. Nevoid Comedones These are rare and may present before or around puberty.52–54 They may increase in size as the patient ages. The lesions may be confluent comedones or whiteheads, usually occurring asymmetrically. A linear distribution is also common. They may be localized or, in some unfortunate individuals, extremely extensive. Treatment is difficult. Response to oral and topical retinoids is unsatisfactory. Physical methods are also generally unsatisfactory, but gentle cautery, excision of locally affected areas, and CO2 laser therapy can be tried; however, as yet there seems no satisfactory solution for most patients. Occasionally inflammatory lesions arise from the comedones, usually after puberty, and this may necessitate treatment with oral and topical antibiotics or benzoyl peroxide. Scarring can arise even from noninflamed lesions.
COMEDONE FORMATION
373
Conglobate Comedones Patients with conglobate acne are predominantly males with extensive truncal acne characterized by severe nodular inflammation and scarring. A hallmark of the disease is grouped comedones,55,56 particularly on the posterior neck and upper trunk. The comedones may be blackheads, whiteheads, or both. This type of acne is extremely difficult to treat; there are no satisfactory data pointing to a preferred approach. It is a question of trying various therapies, particularly topical retinoids combined with oral antibiotics and low-dose oral isotretinoin. Because of the very slow response of these lesions, combination therapy with long-term oral isotretinoin (often low-dose regimes), rotational antibiotics (each for 3– 4 months), topical retinoids, and benzoyl peroxide may be the best approach.
References 1. Holmes RL, Williams M, Cunliffe WJ. Pilo-sebaceous duct obstruction and acne. Br J Dermatol 1972;87:327–32. 2. Pagnoni A, Kligman AM, el-Gammal S, et al. Determination of density of follicles on various regions of the face by cyanoacrylate biopsy: correlation with sebum output. Br J Dermatol 1994;131:862–5. 3. Pierard GE, Pierard-Franchimont C, Goffin V. Digital image analysis of microcomedones. Dermatology 1995;190:99 –103. 4. Plewig G, Fulton JE, Kligman AM. Cellular dynamics of comedo formation in acne vulgaris. Arch Dermatol Forsch 1971;242:12–29. 5. Knaggs HE, Holland DB, Morris C, et al. Quantification of cellular proliferation in acne using the monoclonal antibody Ki-67. J Soc Invest Dermatol 1994;102:89 –92. 6. Hughes BR, Morris C, Cunliffe WJ, et al. Keratin expression in pilosebaceous epithelia in truncal skin of acne patients. Br J Dermatol 1996;134:247–56. 7. Kirokawa I, Mayer de Silva A, Gollnick H, et al. Monoclonal antibody labelling for cytokeratins and filaggrin in the human pilosebaceous unit of normal seborrhoeic and acne skin. J Invest Dermatol 1988;91:566 –71. 8. Knaggs HE, Hughes BR, Morris C, et al. Immunohistochemical study of desmosomes in acne vulgaris. Br J Dermatol 1994;130:731–7. 9. Stewart ME, Wertz PW, Crahek MO. Relationship between sebum secretion rates and the concentration of linoleate in sebum and epidermal lipids. Clin Res 1985;33:684 –8. 10. Wertz PW, Miethke MC, Long SA, et al. The composition of the ceramides from human stratum corneum and from comedones. J Invest Dermatol 1985;84:410 –2. 11. Downing DT, Stewart ME, Wertz PW, et al. Essential fatty acids and acne. J Am Acad Dermatol 1986;14:221–5. 12. Stewart ME, Greenwood R, Cunliffe WJ, et al. Effect of cyproterone acetate-ethinyl estradiol treatment on the proportion of linoleic and sebaceic acids in various skin surface lipid classes. Arch Dermatol Res 1986;278:481–5. 13. Knutson DD. Ultrastructural observations in acne vulgaris: the normal sebaceous follicle and acne lesions. J Invest Dermatol 1974;62:288 –307.
374 CUNLIFFE ET AL.
14. Motoyoshi K. Enhanced comedo formation in rabbit ear skin by squalene and oleic acid peroxides. Br J Dermatol 1983;109:191–8. 15. Woo-Sam PC. Cohesion of horny cells during comedo formation. An electron microscope study. Br J Dermatol 1977;97:609 –15. 16. Kanaar P. Follicular– keratogenic properties of fatty acids in the extemal ear canal of the rabbit. Dermatologica 1971;142:14 –22. 17. Kligman AM, Katz AC. Pathogenesis of acne vulgaris: I. Comedogenic properties of human sebum in extemal ear canal of the rabbit. Arch Dermatol 1968;98:53–7. 18. Frank SB. Is the rabbit ear test in its present state, prophetic of acnegenicity? J Am Acad Dermatol 1982;6:373–7. 19. Mills OH, Kligman AM. A human model for assaying comedolytic substances. Br J Dermatol 1982;107:543–8. 20. Tucker SB, Flannigan SA, Dunbar M, et al. Development of an objective comedogenicity assay. Arch Dermatol 1986;122:699 –702. 21. Zheng P, Gendimenico GJ, Mezick JA, et al. Topical alltransretinoic acid rapidly corrects the follicular abnormalities of the rhino mouse. An ultrastructural study. Acta Derm Venereol (Stockh) 1993;73:97–101. 22. Lucky AW, Biro FM, Huster GA, et al. Acne vulgaris in premenarchal girls. Arch Dermatol 1994;130:310 –4. 23. Choudry R, Hodgins MB, Van der Kavast TH, et al. Localization of androgen receptors in human skin by immunocytochemistry. J Endocrinol 1992;133:467–74. 24. Thiboutot DM, Knaggs H, Gilliland K, et al. Activity of type 1 5␣-reductase is greater in the follicular infrainfundibulum compared with the epidermis. Br J Dermatol 1997;136:166 –71. 25. Thiboutet D, Gilliland K, Light J, et al. Androgen metabolism in sebaceous glands from subjects with and without acne. Arch Dermatol 1999;135:1041–8. 26. Thiboutot D, Bayne El, Thorne J, et al. Immunolocalization of 5␣-reductase isozymes in acne lesions and normal skin. Arch Dermatol 2000;136:1125–9. 27. Guy R, Ridden C, Barth J, et al. Isolation and maintenance of the human pilosebaceous duct: 13-cis retinoic acid acts directly on the duct in vitro. Br J Dermatol 1993;128:242–8. 28. Sanders DA, Philpott MP, Nicolle FV, et al. The isolation and maintenance of the human pilosebaceous unit. Br J Dermatol 1994;131:166 –76. 29. Guy R, Green MR, Kealey T. Modeling acne in vitro. J Invest Dermatol 1996;106:176 –82. 30. Ingham E, Eady A, Goodwin CE, et al. Pro-inflammatory levels of interleukin-1␣–like bioactivity are present in the majority of open comedones in acne vulgaris. J Invest Dermatol 1992;98:895–901. 31. Guy G, Kealey T. The effect of inflammatory cytokines on the isolated human sebaceous infundibulum. J Invest Dermatol 1998;110:410 –5. 32. Downie MMT, Sanders DA, Kealey T. Modeling the remission of individual acne lesions in vitro. Brit J Dermatol 2002;147:869 –78. 33. Lavker RM, Leyden JJ, McCinley KJ. The relationship between bacteria and the abnormal follicular keratinization in acne vulgaris. J Invest Dermatol 1981;77:325–30.
Clinics in Dermatology
Y
2004;22:367–374
34. Leeming JP, Holland KT, Cunliffe WJ. The pathological and ecological significance of microorganisms colonizing acne vulgaris comedones. J Med Microbiol 1985;20:11–6. 35. Aldana OL, Holland DB, Cunliffe WJ. The theory of comedone cycling [abstract]. J Invest Dermatol 1997;108:384. 36. Simpson NB. Functional blockage of open comedones. Br J Dermatol 1987;117:43–7. 37. Williams M, Cunliffe WJ, Gould D. Pilo-sebaceous duct physiology. I. Effect of hydration on pilo-sebaceous duct orifice. Br J Dermatol 1974;90:631–5. 38. Jeremy AHT, Holland DB, Roberts SG, et al. Inflammatory events are involved in acne lesion initiation. J Invest Dermatol 2003;121,20-4. 39. Cunliffe WJ, Holland DB, Clark SM, et al. Comedogenesis: some new aetiological, clinical and therapeutic strategies. Br J Dermatol 2000;142:1084 –91. 40. Norris JF, Cunliffe WJ. A histological and immunocytochemical study of early acne lesions. Br J Dermatol 1988; 118:651–9. 41. Pepall LM, Cosgrove MP, Cunliffe WJ. Ablation of whiteheads by cautery under topical anaesthesia. Br J Dermatol 1991;125:256 –9. 42. Bottomley WW, Yip J, Knaggs H, et al. Treatment of closed comedones: comparisons of fulguration with topical tretinoin and electrocautery with fulguration. Dermatology 193;186:253-7. 43. Yip J, Pepall LM, Gawkrodger DJ, et al. Light cautery and EMLA in the treatment of chloracne lesions. Br J Dermatol 1993;128:313–6. 44. Plewig G, Kligman AM. Induction of acne by topical steroids. Arch Dermatol Forsch 1973;247:29 –52. 45. Monk B, Cunliffe WJ, Layton AM, et al. Acne induced by inhaled corticosteroids. Clin Exp Dermatol 1993;18:148 –50. 46. White G Jr, Tyler LS. Blackmarket steroids complicate acne therapy [letter]. J Fam Pract 1987;25:214. 47. Fyrand O, Fiskdaadal HJ, Trygstad O. Acne in pubertal boys undergoing treatment with androgens. Acta Derm Venereol (Stockh) 1992;72:148 –9. 48. Crow KD. Chloracne and its potential clinical implications. Clin Exp Dermatol 1981;6:243–57. 49. Rosas-Vasquez E, Campos-Macias P, Ochoa-Tirado JG, et al. Chloracne in the 1990s. Int J Dermatol 1996;35:643–5. 50. McConnell R, Anderson K, Russell W, et al. Angiosarcoma, porphyria cutanea tarda and probable chloracne in a worker exposed to waste oil contaminated with a 2,3,7,8-tetrachorodibenzo--dioxin. Br J Ind Med 1993;50:699 –703. 51. Coenraads PJ, Brouwer A, Olie K, et al. Chloracne. Some recent issues. Dermatol Clin 1994;12:569 –76. 52. Beck MH, Dave VK. Extensive nevus comedonicus. Arch Dermatol 1980;116:1048 –50. 53. Barsky S, Doyle JA, Winkelmann RK. Nevus comedonicus with epidermolytic hyperkeratosis. A report of our cases. Arch Dermatol 1981;117:86 –8. 54. Munro CS, Wilkie AOM. Epidermal mosaicism producing localised acne: somatic mutation in FGFR2. Lancet 1998; 352:704 –5. 55. Burns RE, Colville JM. Acne conglobata with septicemia. Arch Dermatol 1959;79:361–3. 56. Williamson DM, Cunliffe WJ, Gatecliff M, et al. Acute ulcerative acne conglobata (acne fulminans) with erythema nodosum. Clin Exp Dermatol 1977;2:351–4.
Etiologic Aspects of Comedogenesis
Reasons for Ductal Hyperproliferation
C
Several factors have been implicated in the induction of ductal keratinocyte hyperproliferation, including abnormalities in sebaceous lipid composition, androgens, local cytokine production, and bacteria.
From the Skin Research Centre, University of Leeds, Leeds, UK. Address correspondence to Dr. William J. Cunliffe, General Infirmary at Leeds, Department of Dermatology, Great George Street, Leeds LS1 3EX, UK. E-mail address: [email protected]
Abnormalities in Sebaceous Lipids Sebaceous lipids are unique to humans and are very complex. They consist predominantly of squalene, wax esters, and triglycerides, which, when metabolized by cutaneous bacterial lipases, produce a complex array of free fatty acids. Of the abnormal sebaceous lipids in acne patients, linoleate levels may be relevant. Examination of polar lipids recovered from comedones shows that the acyl ceramides contain only 6% linoleate among the esterified fatty acids, compared with 45% in normal human epidermis.9 –11 Linoleic acid is reduced in sebum from acne subjects, but returns to normal with resolution of acne after treatment with oral isotretinoin and oral antiandrogens.12 A low level of linoleate also results in a decreased epidermal barrier function, which might render the comedonal wall permeable to inflammatory substances. Membrane-coated granules13–15 are probably more related to barrier permeability than to cell separation and are decreased in comedones, but the significance of this finding remains unclear. Other lipids have been incriminated in comedone formation; in particular, an increase in other free fatty acids and squalene have been blamed for inducing comedones.14,16,17 This has been demonstrated in the rabbit-ear model;18 however, the development of a human model for comedogenesis has suggested that the rabbit model may be inappropriately overreactive.19
omedones result from abnormalities in the proliferation and differentiation of ductal keratinocytes. Comedones represent the retention of hyperproliferating ductal keratinocytes/corneocytes in the duct. This hyperproliferation has been confirmed by demonstration of an increase in 3H-thymidine labeling of comedones4 and an increase in the Ki-67 labeling of ductal keratinocytes.5 This technique has also demonstrated an increase in the proliferation of ductal keratinocytes of “nonaffected” follicles, which were biopsied as clinically “normal” follicles from an area affected by acne.5 This fits with the histological observation of microcomedones being found in 30% of (serially sectioned) tissue sections of clinically “normal” skin taken from around acne lesions. Further evidence of ductal hyperproliferation is the presence of keratins 6 and 16 (keratin markers of hyperproliferation) in microcomedones and comedones.6 The primary abnormality that gives rise to hypercornification is not related to changes in keratin expression.7 Comedogenesis could also be due to the failure of ductal keratinocytes to adequately separate. Studies of involucrin expression and desmosomes, which are features of terminal differentiation, have shown no difference between follicles from acne and control biopsy specimens.8 More research is required on this important issue of ductal corneocyte adhesion.
© 2004 by Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010
0738-081X/04/$–see front matter doi:10.1016/j.clindermatol.2004.03.011
368 CUNLIFFE ET AL.
Clinics in Dermatology
Y
2004;22:367–374
Figure 1. A microcomedone.
Laboratory animals do not develop whiteheads or inflamed acne lesions, even though the rabbit ear readily produces comedones.17 The rhino mouse is an alternative useful model for comedogenesis.20,21 It is important emphasize that neither of these animal models demonstrated inflammation, which frequently occurs in humans. Androgen Control of Comedogenesis Evidence is now accumulating suggesting that androgens may play an important role in comedogenesis. There is a correlation between comedone numbers in early acne and DHEAS levels in prepubertal individuals.22 Comedones are frequently seen before puberty and often precede the development of inflammation by several months or even 1–2 years (Fig 2). Cells of the pilosebaceous duct have androgen receptors,23 and 5␣reductase type I is also present in these cells in both health and disease.24 –26 Antiandrogen-containing drugs, such as cyproterone acetate in the drug co-cyprindiol (Dianette, Estelle 35), reduce comedones. Co-
Figure 2. This prepubertal female exhibits inflammatory lesions. These were preceded for 2 years by blackheads.
Figure 3. A normal pilosebaceous duct grown in vitro. (With permission from Dr. Terence Kealey).
cyprindiol also increases sebaceous linoleate concentration,12 and thus antiandrogen therapy could modulate comedogenesis both directly and indirectly by influencing sebaceous lipids. Cytokines and Comedone Formation Cytokine production by ductal keratinocytes is also likely important in the formation of comedones. Kealey et al27–29 developed an excellent in vitro model for growing the duct. Interleukin (IL)-1␣ is present in many comedones at levels likely to be biologically and pathologically relevant30 and induces comedogenesis (Figs 3 and 4). Furthermore, epidermal growth factor markedly disrupts the duct comedo in vitro.27–32 Kealey et al have provided data to show that the isolated, cultured duct is also a good model for studying the effects of inflammatory cytokines in the etiology of acne. For example, they have shown that epidermal growth factor and transforming growth factor alpha not only affect the pilose-
Clinics in Dermatology
Y
2004;22:367–374
COMEDONE FORMATION
369
Figure 5. This addition of epidermal growth factor in vitro destroys the duct. (With permission from Dr. Terence Kealey.)
opment of comedones. However, bacteria, particularly Propionibacterium acnes, are likely involved later in comedogenesis. Figure 4. This demonstrates that the addition of interleukin-1 alpha can in vitro produce individual a comedone. (With permission from Dr. Terence Kealey.)
baceous duct, but also inhibit sebum production in vitro (Fig 5). 29 Bacteria in Comedogenesis Bacteria are probably not involved in the initiation of comedones. Electron microscopy of early noninflamed lesions taken from prepubertal and early pubertal individuals has demonstrated few or no bacteria.33 Quantification of bacteria from comedones suggests that follicular colonization may be unrelated to comedogenesis.34 Biopsy and culture of early noninflamed lesions has shown that 30% of these are without bacteria,34 suggesting that ductal bacteria are not needed for the initiation of cornification in the devel-
Cycling of Comedones Comedones are temporary structures. This is self- evident to the clinician; otherwise a patient who develops acne at age 11 years and has predominantly comedonal lesions would by late adolescence have a face completely full of such lesions. Clinically this does not happen. Using markers of cell cycling and keratinocyte proliferation, it has been shown that, like the hair follicles, normal pilosebaceous follicles and comedones undergo cyclical growth.35 This cycling phenomenal extends over a period of days or a few weeks rather than, as in the hair follicle, months. Clinical observation on the life cycle of whiteheads show that many whiteheads have resolved within 12 days (Fig 6). Further evidence for the renewal of comedones is that extracted blackheads refill over 2– 6 weeks.
370 CUNLIFFE ET AL.
Figure 6. The lifespan of whiteheads.
Measurements of sebum outflow have demonstrated that functionally some comedones are blocked relatively permanently.36 Others can become blocked temporarily after skin hydration,37 and this obstruction is associated with a decrease in sebum outflow. This observation may explain the precipitation or exacerbation of acne by heat and humidity seen in individuals who work in kitchens and who have traveled in hot, humid environments, such as Majorca, Greece, and the Far East. Certain external chemicals may contribute to comedogenesis. These substances include the ingredients of some cosmetics, such as isopropyl myristate, propylene glycol, and red dyes D and C. Certain drugs applied topically, such as corticosteroids, will also induce comedones, as will other external chemicals, such as chloracnegic agents. Just how such external agents trigger comedogenesis is not adequately understood.
Could Comedone Formation Be Primarily an Inflammatory Process? Recently it has been demonstrated that a significant number of biopsy specimens from the normal-looking
Figure 7. Sandpaper acne; note the presence of many small confluent whiteheads.
Clinics in Dermatology
Y
2004;22:367–374
Figure 8. Extensive macrocomedones.
skin of acne patients that show no evidence of microcomedones or ductal hyperproliferation whatsoever have a significant inflammatory cell infiltrate around the follicle (particularly CD3⫹ and CD4⫹ cells and macrophages).38 For many years dermatologists have been aware, based on data from clinical trials and their own clinical perception, that antimicrobial agents significantly reduce comedonal lesions. This observation by Jeremy et al38 adequately explains this clinical observation, because these inflammatory cells are significantly suppressed by antimicrobial therapy. Thus this explains why such therapies significantly reduce comedones.
The Pilosebaceous Duct Is Not a Hollow Tube Some physicians consider the pilosebaceous duct to be similar to the sweat gland duct in terms of the internal lumenal structure. This is not the case, however. Rather, the pilosebaceous duct is a morass of multiple, intertwining canaliculi, not all of which are connected to the external skin surface. The canaliculi are composed of desquamating corneocytes and sebaceous secretions.
Figure 9. Very large macrocomedones behind the ear.
Clinics in Dermatology
Y
2004;22:367–374
The canaliculi contain are even more degenerated corneocytes, sebum, and bacteria.
Clinical Presentation of Comedones Comedone Types The clinical type of comedo should influence the choice of treatment. It is important that the physician recognize the different types of comedonal lesions and treat them appropriately.39 In most patients, several types of comedones coexist. Microcomedones Microcomedones are histological observations. They can be detected on skin surface biopsy, and their numbers correlate with acne severity.1–3 Serially cut biopsy sections of normal-looking skin in an acne-prone individual will frequently (28%) demonstrate histological features of microcomedones.39 Evaluation of biopsy specimens of papules obtained up to 72 hours after development will reveal a microcomedone in 52% of subjects, a whitehead in 22%, and a blackhead in 10%.40 This finding clearly confirms the practical need to apply topical therapies to apparently noninvolved skin as well as to active acne lesions. Ordinary Comedones Dermatologists recognize the typical pattern of commonly seen comedones (blackheads and whiteheads), and this requires little additional explanation except to stress that whiteheads are usually present in much greater numbers than blackheads. A good light is needed to adequately assess just how many whiteheads most acne patients have. Whiteheads are an essential feature of the clinical picture and thus play a vital role in the development of inflammation. They must be optimally treated; the first choice should be a topical retinoid. Missed Comedones Physicians frequently underestimate the number of comedones. In all patients, it is essential to stretch the skin, using a good light, at a shallow angle; otherwise some comedones may go unrecognized. In about 30% of patients, stretching the skin will reveal comedones that otherwise cannot be seen, thus allowing the prescription of appropriate topical therapy (a topical retinoid). The treatment protocols for ordinary, “missed,” and microcomedones are similar. The topical treatment must be applied not just to the lesions, but also to the adjacent subclinical “normal” skin. Physical methods of therapy, such as blackhead removers, are worthy of consideration in those patients with obvious blackheads, especially if present over a firm, bony surface. Data from numerous clinical trials, some of which are reported elsewhere in this issue, indicate that topical retinoids reduce comedones by 60% after 3 months of therapy. Topical retinoids are an essential part of
COMEDONE FORMATION
371
topical therapy for most acne patients. Topical azaleic acid and salicylic acid also have anticomedonal effects; these agents, as well as topical retinoids, are described in detail in other articles in this issue. The potential for benzoyl peroxide to reduce comedones is often questioned. However, data from clinical trials clearly show that benzoyl peroxide reduces comedones as well as topical retinoids. With topical antibiotics, the reduction in comedones after 3 months of treatment is on the order of 30 – 40%. One of the earliest features in comedone formation is a significant lymphocyte infiltrate around the follicle occurring before any clinical or microscopic evidence of comedones is apparent.38 Antimicrobial therapy for acne also has a direct anti-inflammatory activity against the type of lymphocyte infiltrate present in the precomedonal lesions so described.38 This may explain why antimicrobial therapy reduces comedones. Sandpaper Comedones These predominantly small, closed comedones are almost confluent, giving the skin a “sandpaper” feel (Fig 7). 39 They occur predominately on the forhead and cheek, and often develop into small, inflamed lesions.39 Sandpaper comedones are difficult to treat; on the whole, they show little or variable response to oral antibiotics and topical retinoids. The optimum treatment is oral isotretinoin at a preferred dosage of .5 mg/kg⫺1/daily. Macrocomedones This term refers to blackheads and whiteheads that are ⬎1 mm in size (Fig 8). Macrocomedones occur much more frequently as whiteheads than blackheads. They need to be treated for two reasons. They are a cosmetic problem and may flare into inflamed lesions, particularly in patients treated with oral isotretinoin. In such patients, they are a significant reason for a severe flare of the acne. Macrocomedones are easily missed unless adequate lighting is used and the skin is stretched. The optimum therapy is gentle cautery.41– 43 This is performed under topical local anesthesia using an anesthetic cream such as EMLA, which is applied for 60 –75 minutes under an occlusive dressing such as Tegaderm. The area is then lightly touched with a small hot-wire cautery probe, with the tip gray in color rather than vividly red-hot. The temperature of the cautery should be just high enough to char a paper towel. The purpose is not to significantly burn the skin, but rather to produce low-grade localized thermal damage from the influx of polymorphonucleocytes. This therapy is far superior to topical retinoids; 2 weeks of treatment using light cautery typically produces virtually 100% clearance, In comparison, topical retinoid therapy typically produces ⬍10% reduction (Figs 9 and 10).42 Not all patients respond perfectly; 40% develop recurrent lesions necessitating multiple treatments with
372 CUNLIFFE ET AL.
Clinics in Dermatology
Y
2004;22:367–374
Figure 11. Pomade acne. Note the presence of many whiteheads
depending on how many submarine comedones are present. The comedones are surprisingly quite large, possibly as large as 1 cm. Treatment is difficult; the optimum therapy is probably the gentle cautery de-
Figure 10. The same patient after two sessions of treatment with gentle cautery.
gentle cautery. If the patient is receiving oral isotretinoin and the acne has flared as a consequence of the macrocomedones, then it is necessary to either stop the oral isotretinoin temporarily or reduce the dosage by about 50% until the physical therapy is completed. In such circumstances, a short course of oral corticosteroids (eg, .5 mg/kg daily for 2–3 weeks) may be needed. In all patients treated with gentle cautery, a test area is always treated initially, and thereafter the remaining lesions are treated in further sessions at 2- to 3-week intervals. Scarring and pigment changes are uncommon. Macrocomedones are also a cause of a slow and poor response to oral isotretinoin therapy.44 Submarine Comedones These uncommon types of comedones are easily missed. It is often necessary to stretch the skin to make the correct diagnosis. They usually present as a focus of repeated inflammation at the same site. The inflammation is usually in the form of a nodule or nodules,
Figure 12. Numerous blackheads typical of chloracne.
Clinics in Dermatology
Y
2004;22:367–374
scribed previously for treating macrocomedones. In such patients, the surface of the submarine comedone is gently touched with the cautery at 10 –12 sites over the surface of the large comedone. This procedure stimulates a polymorphonucleocyte response and so allows subsequent drainage of retained corneocytes from the comedone. This technique is successful in about 50% of submarine comedones. The correct Drug-Induced Comedones and Pomade Comedones Drug-induced comedones may result from oral, topical, intranasal, or interthecal corticosteroids44,45 or oral anabolic steroids.46,47 “Blue comedones” can result, albeit very infrequently, from the development of minocycline-induced pigmentation in noninflamed lesions. This condition can be confused with osteoma cutis. Pomade acne occurs especially in Afro-Caribbeans, who apply certain defrizzing agents to their hair (Fig 11). Treatment of drug-induced comedones and pomade acne involves removing the cause and treating with either topical retinoids or gentle cautery. Chloracne Chloracne is also characterized by many persistent comedones.48 –51 Indeed, comedonal acne is a hallmark of this type, and inflammatory lesions are less frequent (Fig 12). In extensive chloracne, scarring may arise even from noninflammatory lesions. Inflamed lesions may be treated with oral antibiotics, topical benzoyl peroxide, or topical antibiotics. Gentle cautery is relatively successful, but there is usually a poor response to topical and oral retinoids.51 The poor response to oral isotretinoin relates to the fact that chloracne is associated with atrophy of the sebaceous gland, and oral isotretinoin primarily helps acne by dramatically reducing the size and function of the gland. Unfortunately, some patients with chloracne have systemic problems, and the disease may persist for many years despite withdrawal of the chloracne agent. Nevoid Comedones These are rare and may present before or around puberty.52–54 They may increase in size as the patient ages. The lesions may be confluent comedones or whiteheads, usually occurring asymmetrically. A linear distribution is also common. They may be localized or, in some unfortunate individuals, extremely extensive. Treatment is difficult. Response to oral and topical retinoids is unsatisfactory. Physical methods are also generally unsatisfactory, but gentle cautery, excision of locally affected areas, and CO2 laser therapy can be tried; however, as yet there seems no satisfactory solution for most patients. Occasionally inflammatory lesions arise from the comedones, usually after puberty, and this may necessitate treatment with oral and topical antibiotics or benzoyl peroxide. Scarring can arise even from noninflamed lesions.
COMEDONE FORMATION
373
Conglobate Comedones Patients with conglobate acne are predominantly males with extensive truncal acne characterized by severe nodular inflammation and scarring. A hallmark of the disease is grouped comedones,55,56 particularly on the posterior neck and upper trunk. The comedones may be blackheads, whiteheads, or both. This type of acne is extremely difficult to treat; there are no satisfactory data pointing to a preferred approach. It is a question of trying various therapies, particularly topical retinoids combined with oral antibiotics and low-dose oral isotretinoin. Because of the very slow response of these lesions, combination therapy with long-term oral isotretinoin (often low-dose regimes), rotational antibiotics (each for 3– 4 months), topical retinoids, and benzoyl peroxide may be the best approach.
References 1. Holmes RL, Williams M, Cunliffe WJ. Pilo-sebaceous duct obstruction and acne. Br J Dermatol 1972;87:327–32. 2. Pagnoni A, Kligman AM, el-Gammal S, et al. Determination of density of follicles on various regions of the face by cyanoacrylate biopsy: correlation with sebum output. Br J Dermatol 1994;131:862–5. 3. Pierard GE, Pierard-Franchimont C, Goffin V. Digital image analysis of microcomedones. Dermatology 1995;190:99 –103. 4. Plewig G, Fulton JE, Kligman AM. Cellular dynamics of comedo formation in acne vulgaris. Arch Dermatol Forsch 1971;242:12–29. 5. Knaggs HE, Holland DB, Morris C, et al. Quantification of cellular proliferation in acne using the monoclonal antibody Ki-67. J Soc Invest Dermatol 1994;102:89 –92. 6. Hughes BR, Morris C, Cunliffe WJ, et al. Keratin expression in pilosebaceous epithelia in truncal skin of acne patients. Br J Dermatol 1996;134:247–56. 7. Kirokawa I, Mayer de Silva A, Gollnick H, et al. Monoclonal antibody labelling for cytokeratins and filaggrin in the human pilosebaceous unit of normal seborrhoeic and acne skin. J Invest Dermatol 1988;91:566 –71. 8. Knaggs HE, Hughes BR, Morris C, et al. Immunohistochemical study of desmosomes in acne vulgaris. Br J Dermatol 1994;130:731–7. 9. Stewart ME, Wertz PW, Crahek MO. Relationship between sebum secretion rates and the concentration of linoleate in sebum and epidermal lipids. Clin Res 1985;33:684 –8. 10. Wertz PW, Miethke MC, Long SA, et al. The composition of the ceramides from human stratum corneum and from comedones. J Invest Dermatol 1985;84:410 –2. 11. Downing DT, Stewart ME, Wertz PW, et al. Essential fatty acids and acne. J Am Acad Dermatol 1986;14:221–5. 12. Stewart ME, Greenwood R, Cunliffe WJ, et al. Effect of cyproterone acetate-ethinyl estradiol treatment on the proportion of linoleic and sebaceic acids in various skin surface lipid classes. Arch Dermatol Res 1986;278:481–5. 13. Knutson DD. Ultrastructural observations in acne vulgaris: the normal sebaceous follicle and acne lesions. J Invest Dermatol 1974;62:288 –307.
374 CUNLIFFE ET AL.
14. Motoyoshi K. Enhanced comedo formation in rabbit ear skin by squalene and oleic acid peroxides. Br J Dermatol 1983;109:191–8. 15. Woo-Sam PC. Cohesion of horny cells during comedo formation. An electron microscope study. Br J Dermatol 1977;97:609 –15. 16. Kanaar P. Follicular– keratogenic properties of fatty acids in the extemal ear canal of the rabbit. Dermatologica 1971;142:14 –22. 17. Kligman AM, Katz AC. Pathogenesis of acne vulgaris: I. Comedogenic properties of human sebum in extemal ear canal of the rabbit. Arch Dermatol 1968;98:53–7. 18. Frank SB. Is the rabbit ear test in its present state, prophetic of acnegenicity? J Am Acad Dermatol 1982;6:373–7. 19. Mills OH, Kligman AM. A human model for assaying comedolytic substances. Br J Dermatol 1982;107:543–8. 20. Tucker SB, Flannigan SA, Dunbar M, et al. Development of an objective comedogenicity assay. Arch Dermatol 1986;122:699 –702. 21. Zheng P, Gendimenico GJ, Mezick JA, et al. Topical alltransretinoic acid rapidly corrects the follicular abnormalities of the rhino mouse. An ultrastructural study. Acta Derm Venereol (Stockh) 1993;73:97–101. 22. Lucky AW, Biro FM, Huster GA, et al. Acne vulgaris in premenarchal girls. Arch Dermatol 1994;130:310 –4. 23. Choudry R, Hodgins MB, Van der Kavast TH, et al. Localization of androgen receptors in human skin by immunocytochemistry. J Endocrinol 1992;133:467–74. 24. Thiboutot DM, Knaggs H, Gilliland K, et al. Activity of type 1 5␣-reductase is greater in the follicular infrainfundibulum compared with the epidermis. Br J Dermatol 1997;136:166 –71. 25. Thiboutet D, Gilliland K, Light J, et al. Androgen metabolism in sebaceous glands from subjects with and without acne. Arch Dermatol 1999;135:1041–8. 26. Thiboutot D, Bayne El, Thorne J, et al. Immunolocalization of 5␣-reductase isozymes in acne lesions and normal skin. Arch Dermatol 2000;136:1125–9. 27. Guy R, Ridden C, Barth J, et al. Isolation and maintenance of the human pilosebaceous duct: 13-cis retinoic acid acts directly on the duct in vitro. Br J Dermatol 1993;128:242–8. 28. Sanders DA, Philpott MP, Nicolle FV, et al. The isolation and maintenance of the human pilosebaceous unit. Br J Dermatol 1994;131:166 –76. 29. Guy R, Green MR, Kealey T. Modeling acne in vitro. J Invest Dermatol 1996;106:176 –82. 30. Ingham E, Eady A, Goodwin CE, et al. Pro-inflammatory levels of interleukin-1␣–like bioactivity are present in the majority of open comedones in acne vulgaris. J Invest Dermatol 1992;98:895–901. 31. Guy G, Kealey T. The effect of inflammatory cytokines on the isolated human sebaceous infundibulum. J Invest Dermatol 1998;110:410 –5. 32. Downie MMT, Sanders DA, Kealey T. Modeling the remission of individual acne lesions in vitro. Brit J Dermatol 2002;147:869 –78. 33. Lavker RM, Leyden JJ, McCinley KJ. The relationship between bacteria and the abnormal follicular keratinization in acne vulgaris. J Invest Dermatol 1981;77:325–30.
Clinics in Dermatology
Y
2004;22:367–374
34. Leeming JP, Holland KT, Cunliffe WJ. The pathological and ecological significance of microorganisms colonizing acne vulgaris comedones. J Med Microbiol 1985;20:11–6. 35. Aldana OL, Holland DB, Cunliffe WJ. The theory of comedone cycling [abstract]. J Invest Dermatol 1997;108:384. 36. Simpson NB. Functional blockage of open comedones. Br J Dermatol 1987;117:43–7. 37. Williams M, Cunliffe WJ, Gould D. Pilo-sebaceous duct physiology. I. Effect of hydration on pilo-sebaceous duct orifice. Br J Dermatol 1974;90:631–5. 38. Jeremy AHT, Holland DB, Roberts SG, et al. Inflammatory events are involved in acne lesion initiation. J Invest Dermatol 2003;121,20-4. 39. Cunliffe WJ, Holland DB, Clark SM, et al. Comedogenesis: some new aetiological, clinical and therapeutic strategies. Br J Dermatol 2000;142:1084 –91. 40. Norris JF, Cunliffe WJ. A histological and immunocytochemical study of early acne lesions. Br J Dermatol 1988; 118:651–9. 41. Pepall LM, Cosgrove MP, Cunliffe WJ. Ablation of whiteheads by cautery under topical anaesthesia. Br J Dermatol 1991;125:256 –9. 42. Bottomley WW, Yip J, Knaggs H, et al. Treatment of closed comedones: comparisons of fulguration with topical tretinoin and electrocautery with fulguration. Dermatology 193;186:253-7. 43. Yip J, Pepall LM, Gawkrodger DJ, et al. Light cautery and EMLA in the treatment of chloracne lesions. Br J Dermatol 1993;128:313–6. 44. Plewig G, Kligman AM. Induction of acne by topical steroids. Arch Dermatol Forsch 1973;247:29 –52. 45. Monk B, Cunliffe WJ, Layton AM, et al. Acne induced by inhaled corticosteroids. Clin Exp Dermatol 1993;18:148 –50. 46. White G Jr, Tyler LS. Blackmarket steroids complicate acne therapy [letter]. J Fam Pract 1987;25:214. 47. Fyrand O, Fiskdaadal HJ, Trygstad O. Acne in pubertal boys undergoing treatment with androgens. Acta Derm Venereol (Stockh) 1992;72:148 –9. 48. Crow KD. Chloracne and its potential clinical implications. Clin Exp Dermatol 1981;6:243–57. 49. Rosas-Vasquez E, Campos-Macias P, Ochoa-Tirado JG, et al. Chloracne in the 1990s. Int J Dermatol 1996;35:643–5. 50. McConnell R, Anderson K, Russell W, et al. Angiosarcoma, porphyria cutanea tarda and probable chloracne in a worker exposed to waste oil contaminated with a 2,3,7,8-tetrachorodibenzo--dioxin. Br J Ind Med 1993;50:699 –703. 51. Coenraads PJ, Brouwer A, Olie K, et al. Chloracne. Some recent issues. Dermatol Clin 1994;12:569 –76. 52. Beck MH, Dave VK. Extensive nevus comedonicus. Arch Dermatol 1980;116:1048 –50. 53. Barsky S, Doyle JA, Winkelmann RK. Nevus comedonicus with epidermolytic hyperkeratosis. A report of our cases. Arch Dermatol 1981;117:86 –8. 54. Munro CS, Wilkie AOM. Epidermal mosaicism producing localised acne: somatic mutation in FGFR2. Lancet 1998; 352:704 –5. 55. Burns RE, Colville JM. Acne conglobata with septicemia. Arch Dermatol 1959;79:361–3. 56. Williamson DM, Cunliffe WJ, Gatecliff M, et al. Acute ulcerative acne conglobata (acne fulminans) with erythema nodosum. Clin Exp Dermatol 1977;2:351–4.