- Email: [email protected]
Dry skin and skin moisturizers
5
Dry Skin and Skin Moisturizers
Thomas S. SDencer. PhD
Frm Cygnus Research Corporatim Redwood City, California
The patient perceives dry skin to be rough, dry, scaly, and cracked, sometimes feeling the onset of subclinical symptoms before obvious outward clinical manifestation is apparent. More accurately, the clinician may describe dry skin or xerosis as roughened, scaling skin with possibly some cracking. The patient may also experience pruritis and reddening associated with the dry skin, but basically it is a noninflammatory condition. Patients as consumers spend several hundred million dollars a year for skin-care products to moisturize dry skin. Some of these products are highly effective in alleviating the symptoms of dry skin, allowing the skin to return to a normal condition, whereas other products are not effective. The clinician sees a host of skin problems like eczema, chapping, seborrheic dermatitis, itchyosis, mild psoriasis, and atopic dermatitis that all have the same scaling, flaking, and roughness associated with dry skin. In the process of treating these various dermatoses, it is sometimes desirable to use adjunctive therapy to alleviate the scaling and flaking symptoms to make the patient more comfortable. Some effective skin moisturizers will alleviate the discomfort associated with dry skin symptoms and restore pliability and moisture to the stratum corneum while appropriate treatment is used to resolve the underlying dermatosis. The remainder of the chapter will deal with the use of moisturizers to alleviate dry skin symptoms and restore a normal function to the stratum corneum. The discussion will include the nature of skin conditioning, effective products on the skin, product ingredients, patient compliance, and product use.
Definition of Dry Skin Clinically, dry skin appears as small, whitish scales with possibly some reddening and cracking of the skin.‘-3 In its worst forms, dry skin appears as erythematous and even cracked, bleeding, chapped skin. Histologically, mild forms of dry skin have no apparent differences from normal skin with the exception of slight dermarcation of topographical and uplifting of surface cells in the desquamating layers of the stratum corneum.’ When dry skin is associated with chapping or underlying dermatoses, of course, an inflammatory response is seen with erythema, edema, exudation and crusting. For the most part, the symptoms of dry skin that we will discuss deal with the barrier layer or 24
July-September 1988 Volume 6 Number 3
Moisturizers
stratum corneum. Clumps of keratinocytes that do not undergo normal dishesion from the surface appear as large scales, partially attached to the skin. The reasons for the formation of these scales are not well understood; however, scales sometimes form when skin becomes overly mature due to slow turnover as in aging skin.4 In addition, scaling skin can occur with sun damage; immature cells at the skin’s surface, as in psoriasis; or genetic alteration of the desquamation process, as in atopic dermatitis. In all of these cases, a loss of moisture in the surface corneocytes or intercellular lipids results in an outer stratum corneum layer that is mechanically less pliable. The decrease in pliability results in cracking and alteration of the outer layer, propagating cracks through the stratum corneum barrier. Normal flexing of damaged, less pliable skin increases scaling and cracking. In addition, soaps, detergents and lipid solvents contribute to the induction process by disrupting the lipid bilayers between layers of the stratum corneum.s The complexities of dry skin are best explained by considering external factors that may actually induce dry skin. The first thing to understand is the physiology of the stratum corneum layer as individual keratinocytes joined by complex lipid bilayers. The protein lipid matrix within the keratinocyte requires moisture to remain pliable.697Loss of moisture in this matrix causes the stratum corneum to become stiff, nonpliable, and therefore subject to microscopic mechanical breaks during cold, dry weather.197For the most part, except in the case of severe solvent extraction followed by aqueous washing of the skin with soap, the lipid-keratin structure is not denatured by normal environmental factors. Extreme situations, such as washing the hand with gasoline or mineral spirits followed by soap and water washing of the hands, may lead to disruption of the protein keratin matrix within the stratum corneum. The second factor in dry skin is the intercellular lipid bilayer structure. This structure is more accessible to solvents applied to the skin surface. In addition to solvent systems, detergents, soaps, and household cleaners applied to the skin will effectively solubilize the intercel-
25
lular lipid layers between corneocytes in the stratum corneum.* Casesof malnutrition resulting in linoleic acid deficiency have their greatest effect on these lipid bilayers. Loss of barrier function to water loss and rough, scaling skin result from linoleic acid deficiency. Linoleic acid is believed to form anchoring crosslinks across the lipid bilayers. In animal models, topical application of linoleic acid restores the skin barrier function within hours, presumably by reforming intercellular lipid bilayers. More recently, evidence has been found that formation and maintenance of these lipid bilayers that bind cells toghether requires a pH range defined nominally by the normal pH range of the skin, ie, 4.5 to 6.0 pH.9 Therefore, the buffer capacity of the skin that has been discussed for years in the literature, may play a role in the ability of the skin to tolerate repeated insult with surfactants or to resolve damage to the bilayers once the damage has occurred. The role of pH may be to allow lipid bilayers to reform in a manner in which they retain moisture and pliability and maintain adhesion of corneocytes. Blophpical Properties Biophysically, the damaged stratum corneum has a torturous microscopic surface due to scaling and cracking. In addition, low moisture content will make the skin less pliable’0 and cause the dry scales to act as microscopic lever arms to activate nerve fibers nearer the skin’s surface, resulting in an irritant or itching sensation. Deeper cracks or fisures will allow wind and cold to stimulate similar sensations, thereby resulting in winter-itch, excoriation, and patient discomfort. Mechanically, the skin will have a lower frictional component because the hard, rough surface area reduces the contact between the skin and a measuring surface.11 In severe dry skin, the skin becomes hardenedlo; normal transepidermal water loss is elevated because the barrier function of the stratum corneum is altered, the electrical impedance of the skin is greatly increased, and skin pH may be elevated toward the pH of blood serum, 7.4. Under these circumstances, if transparent cellophane type is applied to the skin
26
T. S. Stxncer
surface, large irregular patches of cells can be visualized when the tape is removed from the skin. Normal skin, however, provides an even pattern of very fine scales.
External Factors One causal factor in the formation of dry skin that is often overlooked is the cycling phenomenon. When the skin is exposed to repetitive cycles of high moisture followed by extreme cold (or warm) dryness, the skin is very easily damaged. In the summer, this is caused by dry central air conditioning followed by warm, moist, air outdoors, only to be recycled through cold air conditioning in a car or office.1 In the winter, outdoor exercise resulting in sweating followed by chilling and low indoor relative humidity can induce the cycling effect. In addition, skin stress is exacerbated by mechanical trauma of the skin that abrades the skin’s surface, resulting in damage to the stratum corneum. The unsuspecting patient can even induce the cycing phenomenon by trying to protect his skin from the environment before going outdoors. For instance, application of an excellent hand and body lotion just prior to leving the house will expose very wet skin to the drying effects of cold, winter wind in which the skin is made colder by the evaporation of moisture from the surface. Thus, the physician must remember to remind his patient that not only showers, but simply applying a water-based product to the skin immediately before leaving the house can be detrimental. The evaporation effect can be avoided by applying facial-care or hand-care products at least 30 minutes before going out into a cold, dry environment.
How Moisturizing lotions Work Treatment of dry skin symptoms is accomplished by moisturization and occlusion to provide the skin with water content and pliability, whereas normal epidermal turnover allows the body to produce a normalized stratum corneum barrier. Most oil-in-water lotion and cream moisturizing products provide the skin with a large dose of water that hydrates the skin during the application process. Occlusive
Clinics in D0rmatOlOQY
ingredients in the better lotion products form a barrier over the skin’s surface that reduces transepidermal water loss, allowing the skin to retain the moisture that naturally transpires through the skin. Humectants provide the stratum corneum the the capacity to retain water in locations in the stratum corneum that promote pliability and flexibility. Lubricants in products reduce friction and the frictional component in causing dry skin. Other factors in the products can help the skin retain normal pH, thereby providing an environment in which the lipid bilayers in the skin can more readily normalize and reestablish their capacity to bind corneocytes together and to retain moisture in the intercellular spaces. Other ingredients in lotions provide sensory effects that make the product pleasant to apply, easy to rub into the skin, and pleasant smelling. The importance of these sensory factors is patient compliance, because a product applied once a day due to poor cosmetic attributes will be less effective than a product that patient enjoys applying several times a day. Higher patient compliance will result in more frequent application, maintenance of a constant stratum corneum barrier function, and an optimal skin environment for recovering from the dry skin symptoms.
Composition of Moisturizing lotions Skin attributes like moisturization, mechanical pliability, and skin feel can be improved with a number of personal-care products. These products contain moisturizers; occlusives; lubricants; emollients to improve texture, rub-in properties and softness; and fragrances to improve consumer acceptance of the product. Moisturizers as a class include humectants and occlusives. Humectants are substances that, when absorbed, help the skin retain moisture, thereby making the skin more pliable and softer. Common humectants include glycerin, propylene glycol, pyrrolidone carboxyilic acid, sodium lactate, urea, and certain natural lipid mixtures. More exotic humectants include certain proteins, gelatin, hyaluronic acid, vitamins and some natural ingredients. In general, the humectants act by penetrating into the
July-September1988 Volume6 Number3
Moisturizers
stratum corneum and increasing the amount of moisture that is held in close association with the stratum corneum lipids or proteins. This increased water content provides the stratum corneum with a softer feel, greater flexibility, better mechanical strength, and tends to smooth the scales on the skin’s surface. Most humectants are not as effective as occlusives in protecting the skin from extremely dry, cold winter environments especially under those circumstances where the skin is exposed to windy conditions. Occlusive moisturizers are substances that coat the skin, allowing the skin to maintain its own natural moisture. The partially permeable barrier provided by occlusives allows the skin to trap moisture that is normally transpired to the atmosphere, and reduces evaporative loss of moisture from the surface of the skin due to wind or extremely warm, dry air. Occlusives include substances like petrolatum, lanolin alcohols, jojoba oil, cocoa butter, paraffin, cholesterol, heavy lipid mixtures, olive oil, and heavy mineral oil. Light mineral oil acts more as a solvent and does not generally reduce transepidermal water loss. Although occlusives are very effective in making the skin soft and helping the skin retain moisture, they act by trapping water normally transpiring through skin. Therefore, there is a time lag between application and moisturization unless the occlusive is applied immediately after bathing. Occlusives also tend to be sticky and greasy. Therefore, patient compliance with occlusives used in their pure form is not as high as patient compliance for occlusives included in an effective therapeutic hand and body lotion. Once the water has evaporated from the occlusive lotion, the occlusive ingredients will protect the skin from harsh external environments. In lotion formulas containing humectants and occlusives, emollients are used to improve patient acceptance of the formula. In commercial lotions, a large amount of research is conducted on the use of emollients to provide products with more acceptable consumer feel on application. Emollients can include a host of ingredients from silicone oils to cetyl alcohols, cholesterol, mineral oil, silicone oils, some waxy esters, and certain quaternary compounds. Emollients and lubricants provide skin-care
27
products with the appropriate slip, tactile feel, and rub-in properties to encourage the consumer to use the product more liberally and more frequently. Certain quaternary compounds allow substances like petroleum to be combined with glycerin in personal-care products without feeling greasy. The petrolatum-glycerin combination is especially effective in alleviating dry skin. Other compounds that are included in skincare products are substances like colloidal oatmeal, which are designed to alleviate the itching associated with the rough, scaly, dry skin. Colloidal oatmeal combined with other proteins also provides tactile sensation and some capacity for moisturization. Camphor and menthol also are included in skin-care products to alleviate itching. Fragrances can provide skin-care products with greater user acceptance and, therefore, greater patient compliance. In general, however, fragrance-free products that have an acceptable natural aroma are better for dry, sensitive skin than fragranced products. Most major manufacturers are careful to select fragrances that do not cause allergic contact dermitis or irritation, but hypersensitive individuals should use unfragranced moisturizers. Other substances used in personal-care products include vitamin E, vitamin A (and other retinoids), sunflower oil (linoleic acid), biotin, vitamin D, vitamin B, and certain botanical extracts. If some of these substances are present at concentrations sufficient for therapeutic efficacy, effects on the skin physiology can be observed. However, claims cannot be made unless the products are listed as drugs rather than simple cosmetics. Examples of prescription drug products include ammonium lactate as a desquamation agent and all-transretinoic acid, recently discussed as an antiaging drug. With the advent of therapeutic efficacy found in retinoids, desquamating agents, analgesics or antiitch properties, and different emulsification systems, all products, either drug or consumer products, are not the same. Highly therapeutic hand and body lotions may be slightly more greasy and slightly less acceptable to the consumer, but very efficacious for
28
Clinics in Dermatology
T. S. Spencer
severe scaling and flaking conditions. The high degree of occlusiveness may be just what some patients need. Other patients may find better and more extensive usage of lotions that look and feel better on the skin surface. Some hand and body lotion products provide both therapeutic efficacy and consumer acceptance.
Conclusion Skin moisturization can be accomplished with a number of cosmetically very acceptable skin-care lotions available in the marketplace. Although ingredient listings may be similar, differences in emulsion properties of the products provide different therapeutic efficacy and different cosmetic acceptability of the large number of products on the market. Although therapeutic efficacy is important to alleviate the symptoms of dry skin and to protect the skin from further environmental insult, cosmetic acceptability is important to increase patient compliance and use of the product. Patients subject to dry skin should be counselled to avoid frequent changes in environmental conditions, frequent bathing, and use of soap products. In addition, susceptible patients should be advised to wear protective hand and body lotions when going into harsh, external environments and to apply those lotions 30 minutes before leaving the house. Following these procedures will make the patient more
comfortable with the scaling, cracking, itching associated with dry skin.
and
References 1. Chernosky ME. Clinical aspects Cosmet Chem. 1976;27:365-376.
of dry skin. J Sot
2. Seitz JC, Rizer RL, Spencer TS. Photographic standardization of dry skin. J Sot Cosmet Chem. 1984;35:423437. 3. Kantor I, Ballinger WG, Savin RC. Severely dry skin: Clinical evaluation of a highly effective therapeutic lotion. Cutis. 1982;30:410-424, 4. Grove GL, Kligman AM. Age associated changes in human epidermal cell renewal. J Gerontol. 1983;38:137142. 5. Middleton JD. Mechanism of action of surfactants on water binding properties of isolated stratum corneum. J Sot Cosmet Chem. 1969;20:399-412. 6. Blank IH. Factors which influence water content of stratum corneum. J Invest Dermatol. 1952;18:433-440. 7. Soencer TS. Linamen CE. Akers WA. et al. Temnerature dependence of water content of stratum cornehm. Br J Dermatol. 1975;93:159-164. 8. Elias PM, Bonar L, Grayson S, et al. X-ray diffraction analysis of stratum corneum membrane couplets. J Invest Dermatol. 1983;801:213-214. 9. Osborne DW, Friberg SE. Role of stratum corneum lipids as moisture retaining agents. J Dispersion Sci Tech. 1987;8:173-179. 10. Christensen MS, Hargens CW, Nacht S, et al. Viscoelastic properties of intact human skin: Instrumentation, hydration effects, and the contribution of the stratum corneum. J Invest Dermatol. 1977;69:282-286. 11. Highley DR, Coomey M, DenBeste M, et al. Frictional properties of skin. J Invest Dermatol. 1977;69:303-305.
Address for correspondence: Tom S. Spencer, PhD, Director Cygnus Research Corporation, Redwood City, CA 94063.
of Research
and Development,
Dry Skin and Skin Moisturizers
Thomas S. SDencer. PhD
Frm Cygnus Research Corporatim Redwood City, California
The patient perceives dry skin to be rough, dry, scaly, and cracked, sometimes feeling the onset of subclinical symptoms before obvious outward clinical manifestation is apparent. More accurately, the clinician may describe dry skin or xerosis as roughened, scaling skin with possibly some cracking. The patient may also experience pruritis and reddening associated with the dry skin, but basically it is a noninflammatory condition. Patients as consumers spend several hundred million dollars a year for skin-care products to moisturize dry skin. Some of these products are highly effective in alleviating the symptoms of dry skin, allowing the skin to return to a normal condition, whereas other products are not effective. The clinician sees a host of skin problems like eczema, chapping, seborrheic dermatitis, itchyosis, mild psoriasis, and atopic dermatitis that all have the same scaling, flaking, and roughness associated with dry skin. In the process of treating these various dermatoses, it is sometimes desirable to use adjunctive therapy to alleviate the scaling and flaking symptoms to make the patient more comfortable. Some effective skin moisturizers will alleviate the discomfort associated with dry skin symptoms and restore pliability and moisture to the stratum corneum while appropriate treatment is used to resolve the underlying dermatosis. The remainder of the chapter will deal with the use of moisturizers to alleviate dry skin symptoms and restore a normal function to the stratum corneum. The discussion will include the nature of skin conditioning, effective products on the skin, product ingredients, patient compliance, and product use.
Definition of Dry Skin Clinically, dry skin appears as small, whitish scales with possibly some reddening and cracking of the skin.‘-3 In its worst forms, dry skin appears as erythematous and even cracked, bleeding, chapped skin. Histologically, mild forms of dry skin have no apparent differences from normal skin with the exception of slight dermarcation of topographical and uplifting of surface cells in the desquamating layers of the stratum corneum.’ When dry skin is associated with chapping or underlying dermatoses, of course, an inflammatory response is seen with erythema, edema, exudation and crusting. For the most part, the symptoms of dry skin that we will discuss deal with the barrier layer or 24
July-September 1988 Volume 6 Number 3
Moisturizers
stratum corneum. Clumps of keratinocytes that do not undergo normal dishesion from the surface appear as large scales, partially attached to the skin. The reasons for the formation of these scales are not well understood; however, scales sometimes form when skin becomes overly mature due to slow turnover as in aging skin.4 In addition, scaling skin can occur with sun damage; immature cells at the skin’s surface, as in psoriasis; or genetic alteration of the desquamation process, as in atopic dermatitis. In all of these cases, a loss of moisture in the surface corneocytes or intercellular lipids results in an outer stratum corneum layer that is mechanically less pliable. The decrease in pliability results in cracking and alteration of the outer layer, propagating cracks through the stratum corneum barrier. Normal flexing of damaged, less pliable skin increases scaling and cracking. In addition, soaps, detergents and lipid solvents contribute to the induction process by disrupting the lipid bilayers between layers of the stratum corneum.s The complexities of dry skin are best explained by considering external factors that may actually induce dry skin. The first thing to understand is the physiology of the stratum corneum layer as individual keratinocytes joined by complex lipid bilayers. The protein lipid matrix within the keratinocyte requires moisture to remain pliable.697Loss of moisture in this matrix causes the stratum corneum to become stiff, nonpliable, and therefore subject to microscopic mechanical breaks during cold, dry weather.197For the most part, except in the case of severe solvent extraction followed by aqueous washing of the skin with soap, the lipid-keratin structure is not denatured by normal environmental factors. Extreme situations, such as washing the hand with gasoline or mineral spirits followed by soap and water washing of the hands, may lead to disruption of the protein keratin matrix within the stratum corneum. The second factor in dry skin is the intercellular lipid bilayer structure. This structure is more accessible to solvents applied to the skin surface. In addition to solvent systems, detergents, soaps, and household cleaners applied to the skin will effectively solubilize the intercel-
25
lular lipid layers between corneocytes in the stratum corneum.* Casesof malnutrition resulting in linoleic acid deficiency have their greatest effect on these lipid bilayers. Loss of barrier function to water loss and rough, scaling skin result from linoleic acid deficiency. Linoleic acid is believed to form anchoring crosslinks across the lipid bilayers. In animal models, topical application of linoleic acid restores the skin barrier function within hours, presumably by reforming intercellular lipid bilayers. More recently, evidence has been found that formation and maintenance of these lipid bilayers that bind cells toghether requires a pH range defined nominally by the normal pH range of the skin, ie, 4.5 to 6.0 pH.9 Therefore, the buffer capacity of the skin that has been discussed for years in the literature, may play a role in the ability of the skin to tolerate repeated insult with surfactants or to resolve damage to the bilayers once the damage has occurred. The role of pH may be to allow lipid bilayers to reform in a manner in which they retain moisture and pliability and maintain adhesion of corneocytes. Blophpical Properties Biophysically, the damaged stratum corneum has a torturous microscopic surface due to scaling and cracking. In addition, low moisture content will make the skin less pliable’0 and cause the dry scales to act as microscopic lever arms to activate nerve fibers nearer the skin’s surface, resulting in an irritant or itching sensation. Deeper cracks or fisures will allow wind and cold to stimulate similar sensations, thereby resulting in winter-itch, excoriation, and patient discomfort. Mechanically, the skin will have a lower frictional component because the hard, rough surface area reduces the contact between the skin and a measuring surface.11 In severe dry skin, the skin becomes hardenedlo; normal transepidermal water loss is elevated because the barrier function of the stratum corneum is altered, the electrical impedance of the skin is greatly increased, and skin pH may be elevated toward the pH of blood serum, 7.4. Under these circumstances, if transparent cellophane type is applied to the skin
26
T. S. Stxncer
surface, large irregular patches of cells can be visualized when the tape is removed from the skin. Normal skin, however, provides an even pattern of very fine scales.
External Factors One causal factor in the formation of dry skin that is often overlooked is the cycling phenomenon. When the skin is exposed to repetitive cycles of high moisture followed by extreme cold (or warm) dryness, the skin is very easily damaged. In the summer, this is caused by dry central air conditioning followed by warm, moist, air outdoors, only to be recycled through cold air conditioning in a car or office.1 In the winter, outdoor exercise resulting in sweating followed by chilling and low indoor relative humidity can induce the cycling effect. In addition, skin stress is exacerbated by mechanical trauma of the skin that abrades the skin’s surface, resulting in damage to the stratum corneum. The unsuspecting patient can even induce the cycing phenomenon by trying to protect his skin from the environment before going outdoors. For instance, application of an excellent hand and body lotion just prior to leving the house will expose very wet skin to the drying effects of cold, winter wind in which the skin is made colder by the evaporation of moisture from the surface. Thus, the physician must remember to remind his patient that not only showers, but simply applying a water-based product to the skin immediately before leaving the house can be detrimental. The evaporation effect can be avoided by applying facial-care or hand-care products at least 30 minutes before going out into a cold, dry environment.
How Moisturizing lotions Work Treatment of dry skin symptoms is accomplished by moisturization and occlusion to provide the skin with water content and pliability, whereas normal epidermal turnover allows the body to produce a normalized stratum corneum barrier. Most oil-in-water lotion and cream moisturizing products provide the skin with a large dose of water that hydrates the skin during the application process. Occlusive
Clinics in D0rmatOlOQY
ingredients in the better lotion products form a barrier over the skin’s surface that reduces transepidermal water loss, allowing the skin to retain the moisture that naturally transpires through the skin. Humectants provide the stratum corneum the the capacity to retain water in locations in the stratum corneum that promote pliability and flexibility. Lubricants in products reduce friction and the frictional component in causing dry skin. Other factors in the products can help the skin retain normal pH, thereby providing an environment in which the lipid bilayers in the skin can more readily normalize and reestablish their capacity to bind corneocytes together and to retain moisture in the intercellular spaces. Other ingredients in lotions provide sensory effects that make the product pleasant to apply, easy to rub into the skin, and pleasant smelling. The importance of these sensory factors is patient compliance, because a product applied once a day due to poor cosmetic attributes will be less effective than a product that patient enjoys applying several times a day. Higher patient compliance will result in more frequent application, maintenance of a constant stratum corneum barrier function, and an optimal skin environment for recovering from the dry skin symptoms.
Composition of Moisturizing lotions Skin attributes like moisturization, mechanical pliability, and skin feel can be improved with a number of personal-care products. These products contain moisturizers; occlusives; lubricants; emollients to improve texture, rub-in properties and softness; and fragrances to improve consumer acceptance of the product. Moisturizers as a class include humectants and occlusives. Humectants are substances that, when absorbed, help the skin retain moisture, thereby making the skin more pliable and softer. Common humectants include glycerin, propylene glycol, pyrrolidone carboxyilic acid, sodium lactate, urea, and certain natural lipid mixtures. More exotic humectants include certain proteins, gelatin, hyaluronic acid, vitamins and some natural ingredients. In general, the humectants act by penetrating into the
July-September1988 Volume6 Number3
Moisturizers
stratum corneum and increasing the amount of moisture that is held in close association with the stratum corneum lipids or proteins. This increased water content provides the stratum corneum with a softer feel, greater flexibility, better mechanical strength, and tends to smooth the scales on the skin’s surface. Most humectants are not as effective as occlusives in protecting the skin from extremely dry, cold winter environments especially under those circumstances where the skin is exposed to windy conditions. Occlusive moisturizers are substances that coat the skin, allowing the skin to maintain its own natural moisture. The partially permeable barrier provided by occlusives allows the skin to trap moisture that is normally transpired to the atmosphere, and reduces evaporative loss of moisture from the surface of the skin due to wind or extremely warm, dry air. Occlusives include substances like petrolatum, lanolin alcohols, jojoba oil, cocoa butter, paraffin, cholesterol, heavy lipid mixtures, olive oil, and heavy mineral oil. Light mineral oil acts more as a solvent and does not generally reduce transepidermal water loss. Although occlusives are very effective in making the skin soft and helping the skin retain moisture, they act by trapping water normally transpiring through skin. Therefore, there is a time lag between application and moisturization unless the occlusive is applied immediately after bathing. Occlusives also tend to be sticky and greasy. Therefore, patient compliance with occlusives used in their pure form is not as high as patient compliance for occlusives included in an effective therapeutic hand and body lotion. Once the water has evaporated from the occlusive lotion, the occlusive ingredients will protect the skin from harsh external environments. In lotion formulas containing humectants and occlusives, emollients are used to improve patient acceptance of the formula. In commercial lotions, a large amount of research is conducted on the use of emollients to provide products with more acceptable consumer feel on application. Emollients can include a host of ingredients from silicone oils to cetyl alcohols, cholesterol, mineral oil, silicone oils, some waxy esters, and certain quaternary compounds. Emollients and lubricants provide skin-care
27
products with the appropriate slip, tactile feel, and rub-in properties to encourage the consumer to use the product more liberally and more frequently. Certain quaternary compounds allow substances like petroleum to be combined with glycerin in personal-care products without feeling greasy. The petrolatum-glycerin combination is especially effective in alleviating dry skin. Other compounds that are included in skincare products are substances like colloidal oatmeal, which are designed to alleviate the itching associated with the rough, scaly, dry skin. Colloidal oatmeal combined with other proteins also provides tactile sensation and some capacity for moisturization. Camphor and menthol also are included in skin-care products to alleviate itching. Fragrances can provide skin-care products with greater user acceptance and, therefore, greater patient compliance. In general, however, fragrance-free products that have an acceptable natural aroma are better for dry, sensitive skin than fragranced products. Most major manufacturers are careful to select fragrances that do not cause allergic contact dermitis or irritation, but hypersensitive individuals should use unfragranced moisturizers. Other substances used in personal-care products include vitamin E, vitamin A (and other retinoids), sunflower oil (linoleic acid), biotin, vitamin D, vitamin B, and certain botanical extracts. If some of these substances are present at concentrations sufficient for therapeutic efficacy, effects on the skin physiology can be observed. However, claims cannot be made unless the products are listed as drugs rather than simple cosmetics. Examples of prescription drug products include ammonium lactate as a desquamation agent and all-transretinoic acid, recently discussed as an antiaging drug. With the advent of therapeutic efficacy found in retinoids, desquamating agents, analgesics or antiitch properties, and different emulsification systems, all products, either drug or consumer products, are not the same. Highly therapeutic hand and body lotions may be slightly more greasy and slightly less acceptable to the consumer, but very efficacious for
28
Clinics in Dermatology
T. S. Spencer
severe scaling and flaking conditions. The high degree of occlusiveness may be just what some patients need. Other patients may find better and more extensive usage of lotions that look and feel better on the skin surface. Some hand and body lotion products provide both therapeutic efficacy and consumer acceptance.
Conclusion Skin moisturization can be accomplished with a number of cosmetically very acceptable skin-care lotions available in the marketplace. Although ingredient listings may be similar, differences in emulsion properties of the products provide different therapeutic efficacy and different cosmetic acceptability of the large number of products on the market. Although therapeutic efficacy is important to alleviate the symptoms of dry skin and to protect the skin from further environmental insult, cosmetic acceptability is important to increase patient compliance and use of the product. Patients subject to dry skin should be counselled to avoid frequent changes in environmental conditions, frequent bathing, and use of soap products. In addition, susceptible patients should be advised to wear protective hand and body lotions when going into harsh, external environments and to apply those lotions 30 minutes before leaving the house. Following these procedures will make the patient more
comfortable with the scaling, cracking, itching associated with dry skin.
and
References 1. Chernosky ME. Clinical aspects Cosmet Chem. 1976;27:365-376.
of dry skin. J Sot
2. Seitz JC, Rizer RL, Spencer TS. Photographic standardization of dry skin. J Sot Cosmet Chem. 1984;35:423437. 3. Kantor I, Ballinger WG, Savin RC. Severely dry skin: Clinical evaluation of a highly effective therapeutic lotion. Cutis. 1982;30:410-424, 4. Grove GL, Kligman AM. Age associated changes in human epidermal cell renewal. J Gerontol. 1983;38:137142. 5. Middleton JD. Mechanism of action of surfactants on water binding properties of isolated stratum corneum. J Sot Cosmet Chem. 1969;20:399-412. 6. Blank IH. Factors which influence water content of stratum corneum. J Invest Dermatol. 1952;18:433-440. 7. Soencer TS. Linamen CE. Akers WA. et al. Temnerature dependence of water content of stratum cornehm. Br J Dermatol. 1975;93:159-164. 8. Elias PM, Bonar L, Grayson S, et al. X-ray diffraction analysis of stratum corneum membrane couplets. J Invest Dermatol. 1983;801:213-214. 9. Osborne DW, Friberg SE. Role of stratum corneum lipids as moisture retaining agents. J Dispersion Sci Tech. 1987;8:173-179. 10. Christensen MS, Hargens CW, Nacht S, et al. Viscoelastic properties of intact human skin: Instrumentation, hydration effects, and the contribution of the stratum corneum. J Invest Dermatol. 1977;69:282-286. 11. Highley DR, Coomey M, DenBeste M, et al. Frictional properties of skin. J Invest Dermatol. 1977;69:303-305.
Address for correspondence: Tom S. Spencer, PhD, Director Cygnus Research Corporation, Redwood City, CA 94063.
of Research
and Development,