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Tanning with UVB or UVA: An appraisal of risks
219
Iww!3ANDvIEws
Tanning with UVB or UVA: an appraisal of risks B. L. DifTey+ Regional Medical Ph@cs Departmenq Dryburn Hospital, Durham DHl STW (U.K.)
P. M. Farr Department of Dermatorosr/, Royal Victoria In@mary, Newcastle upon m WK.1
NEI 4LP
1. Introduction Prior to the mid-l 970s the only way of achieving a tan from an artificial source was to use a sunlamp. This was invariably an unfiltered medium or high pressure mercury arc lamp which emitted a broad spectrum of optical radiation from WC (200-290 nm) through to visible and IR radiation. Because of the high WC and WB (290-320 nm) emission, exposure times were short, typically a few minutes. These lamps were inefficient in tanning and it was not uncommon for overexposure to occur resulting in acute eye damage or skin erythema and blistering. Following the development of WA (320400 run) fluorescent lamps it became feasible to induce a tan with WA radiation. In the late 1970s and early 1980s it was suggested that a tan induced by WA was safer than that induced by WB. The tanning industry was quick to seize on this perceived benefit of WA and, as a consequence, WA lamps with minimal or no WI3 content were promoted. Whilst we do not condone tanning, we present arguments which indicate that those people who do wish to tan with arti.flcial sources may be better advised to use lamps in which the WB component, rather than the WA component, contributes the major fraction towards tanning. We consider four different types of lamp and discuss the biological and clinical consequences of tanning with lamps in which either WA or WI3 is the dominant wave band.
2. Lamp characteristics The lamps considered are a medium pressure mercury lamp, a type I WA lamp (e.g. Philips TL09), a type II WA lamp (e.g. Philips TLlO, Mutzhas WASUN) and a ‘simulated sunlight’ lamp. The latter lamp is one in which the ratio of WA to WI3 is similar to that in terrestrial sunlight and in which the W irradiance is such that the time required to achieve a minimal erythema is comparable with sunbathing in summer sunshine at mid-latitudes, i.e. +Author to whom correspondence
should be addressed.
220
NJZWSAND VIEWS
TABLE 1 Characteristics of different UV lamps used for tanning Lamp
Mercury arc sunlamp Simulated sunlight lamp Type I UVA lamp Type II UVA lamp
Radiation emission (%) 1 UVA UVB UVC
UVA
UVJ3
UVC
40 95 99 > 99.9
0 20 60 z-90
35 80 40
65 0 0 0
40 5 1
20 0 0 0
Contribution to tanning (96)
about 20 min. The radiation characteristics of the four lamps are summarized in Table 1. 3. Contribution
to tanning
By combining the spectral emission of each of the four lamps with the action spectrum for tanning it can be shown (Table 1) that the UVA and WB components of the lamps have a disproportionate effect on tanning. Since the action spectra for tanning and erythema are similar [ 11, we chose the Commission International de 1’Eclaire (CIE) reference erythema curve [2] in these calculations. Protagonists of UVA tanning have based their approach on the fact that there is a small divergence in the erythema and tanning action spectra at wavelengths longer than about 340 nm [ 31, indicating that it is possible to tan without burning, particularly for skin types III and above. These data have been extrapolated to imply that tanning with UVA is necessarily safer than with UVB, not only in terms of the risk of erythema, but also in respect of long-term effects such as skin cancer. There is little dispute that tanning with mercury lamps is ineffective and that users often end up with red rather than brown skin. However, in subjects who are able to tan well, both UVA sunbeds and natural sunlight (and presumably a ‘simulated sunlight’ lamp) are effective. The latter source, in which UVB is the dominant tanning wave band, has the additional advantage that epidermal hyperplasia develops providing increased endogenous photoprotection [ 41. 4. Risk of acute overexposure The common injuries from mercury arc sunlamp use are erythema and photokeratitis. Since the recommended exposure times with this type of lamp are only a few minutes, injuries most often occur when users fall asleep, neglect to use adequate eye protection or timers fail. With UVA sunbeds and suncanopies the exposure times required to induce a tan are around 30 min per session and so even exposure of up to 1 h is unlikely to result
NEWS AND VIEWS
221
in significant acute effects. Since the UV dose-erythema response characteristics of UVB and UVA radiation are very similar [5], a ‘simulated sunlight’ solarium, requiring exposure times of about 20 min to induce a tan, is likely to be equally safe in terms of erythema. 5. Clinical effects 5.1. Skin fragility and melunoc~tic lesions The widespread popularity of UVA stmbeds, particularly by users at home, has been accompanied by reports of increased skin fragility [6] and the induction of atypical melanocytic lesions [ 71. That these are new syndromes, previously unrecognized with either sunlight exposure alone or long-term exposure to the radiation from mercury arc sunlamps as occurs in psoriatic patients, suggests that the causative stimulus is high dose UVA radiation. 5.2. Photodermutoses The common photosensitivity disorder, polymorphic light eruption (PLE), often appears consequent to UVA sunbed use [8, 91. Although PLE is also induced by natural sunlight, there is good evidence that the precipitating radiation lies mainly in the UVA wave band [lo], and so it might be expected that the incidence of PLE would be higher as a result of tanning with UVA than with UVB. Support for this hypothesis is given by two studies. In one study [8] a sunbed incorporating type I UVA lamps was used and PLE occurred in 4 out of 33 subjects (12%). In a later study [9] using type II UVA lamps (i.e. much less UVEl than in type I UVA lamps), the incidence of PLE among the 31 subjects who took part was considerably higher (42%). Action spectra for photosensitivity caused by topical or systemic administration of drugs and chemicals are known to be principally within the UVA wave band. Consequently, tanning with high doses of UVA radiation is much more likely to result in a drug-induced photosensitive reaction in susceptible individuals than tanning with UVl3. 5.3. Photoaging Approximately one-third of the UVA radiation incident on white skin will penetrate to the dermis, compared with less than 10% of incident UVB. It is damage to dermal tissues which results in the features characteristic of photoaging: visible wrinkles, furrows and leatheriness. Although the relative importance of UVA and UVB for photoaging in human skin is unknown, there is evidence from animal experiments to suggest that tanning with UVA may result in a similar, or possibly greater, risk of photoaging than tanning with UVB [ll]. 5.4. Non-melanoma skin cancer We have no direct knowledge of the action spectrum for the induction of non-melanoma skin cancer in humans, although an action spectrum for
222
NEWSANDVIEW8
photocarcinogenesis in mouse skin has been determined recently (121. The correspondence of this action spectrum and that for tanning in humans [ 1, 31 is close, particularly when allowance is made for the different optics of mouse and human skin [ 131. This similarity has led others to the conclusion that tanning with either UVB or UVA results in risks of non-melanoma skin cancer of a similar order of magnitude [ 131. In other words, the idea that tanning with UVA is safer than with UVB, in terms of non-melanoma skin cancer risk, can no longer be sustained [ 141. 5.5. Melanoma
The use of artificial tanning equipment has been shown to be a weak risk factor in the induction of cutaneous melanoma [ 151. The relationships between melanoma and sunlight exposure are complex, and the action spectrum for the induction of melanoma by UVR is unknown. Although UVE? radiation is considered by some [ 16} to be the wave band primarily responsible, the possibility that the action spectrum for melanoma lies within the UVA, visible or even the near-IR parts of the solar spectrum cannot be discounted [ 171. For this reason it would be unwise to compare the relative risks of tanning with either UVEIor UVA in respect of melanoma. 6. Discussion Exposing the skin to any combination of UV wavelengths is not without risk to health, particularly in those subjects who do not tan or tan poorly. This view is widely held by skin specialists but, despite consequent warnings, a signiflcant number of people are continuing to use artificial sources to acquire a tan that is perceived to be socially desirable. The vast majority are doing so using appliances in which the effective radiation lies mainly or wholly within the UVA wave band. The general acknowledgement that tanning with UVA is safer than with WI3 is reflected in the regulations and advice concerning the manufacture and design of sunbeds given by many national regulatory authorities and consumer groups. On the basis of the arguments presented above, we question this wisdom and suggest that a course of sunbed sessions, undertaken with the intention of tanning, may be achieved with less risk of adverse effects if the lamps used have an emission spectrum in which the effective radiation lies principally in the UVB, rather than the UVA, wave band, like that of terrestrial sunlight.
1 J. A. Parrish, K. F. Jaenicke and R. R. Anderson, Erythema and melanogenesis action spectra of normal human skin, Photo&em. Photobid., 36 (1981) 187-191. 2 A. F. McKinlay and B. L. Diffey,A reference action spectrum for ultraviolet induced erythema in human skin, CIE J., 6 (1987) 17-22. 3 R. W. Gange, Y. K. Park, M. Auletta, NKagetsu, A. D. Blacken and J. A. Parrish, Action spectra for cutaneous responses to ultraviolet radiation, in F. Urbach and R. W. Gange (eds.), The Biological Effects of WA Radiation, Praeger, New York, 1986, pp. 57-85.
NEWSANDVIEWS
223
4 R. W. Gsnge, A. D. Blackett, E. A. Matzinger, B. M. Sutherland and I. E. Kochevar, Comparative protection efficiency of UVA and WB-induced tans against erythema and formation of endonuclease-sensitivesites in DNA by UVB in humanskin,J. Invest. DennatoL, 85 (1985) 362-364. 5 B. L. Diffey, P. M. Farr and A. M. Oakley, Quantitative studies on UVA-induced erythema in human skin, Br. J. DermaioL, I17 (1987) 67-66. 6 P. M. Farr, J. M. Marks, B. L. Diffey and P. Ince, Skin fragility and blistering due to use of sunbeds, Br. Med. J., 296 (1988) 1708-1709. 7 S. K. Jones, H. Moseley and R. M. MacKie, WA-induced melsnocytic lesions, Br. J. DermutoL, I17 (1987) 111-115. 8 M. S. Devgun, B. E. Johnson and C. R. Paterson, Tanning, protection against sunburnand vitamin D formation with a W-A ‘sunbed’, Br. J. DermuZoL, I07 (1982) 275-284. 9 J. K. Rivers, P. G. Norris, G. M. Murphy, A. C. Chu, G. MidgIey et uI., UVA sunbeds: tanning,photoprotection, acute adverse effects and immunologicaIchanges& J. DermatoL, I20 (1989) 767-777. 10 P. M. Farr and B. L. Diffey, Adverse effects of sunscreens in photosensitive subjects, Lancet, i (1989) 429-431. 11 D. L. Bissett, D. P. Hannon and T. V. Orr, Wavelength dependence of histologicaL physical and visible changes in chronicalIy W-irradiated hairlessmouse skin,Photo&em. PhotobioL, 50 (1989) 763-769. 12 H. J. C. M. Sterenborg, Investigations on the action spectrum of tumorigenesisby ultraviolet radiation, Ph.D. Thesis, Utrecht, 1987. 13 L. Roza, R. A. Baan, J. C. van der Leun and L. Kligman, UVA hazards in skin associated with the use of tanning equipment, J. Photochem PhotobioL B: BioL, 3 (1989) 281-287. 14 H. J. C. M. Sterenborg and J. C. van der Leun, Tumorigenesis by a long wavelength UVA source, Photo&em. Photobiol., (1990) 325-330. 15 A. J. Swerdiow, J. S. C. English, R. M. Ma&e, C. J. O’Doherty, J. A. A. Hunter et al., Fluorescent lights, ultraviolet lamps, and risk of cutaneous melanoma, Br. Med. J., 297 (1988) 647-650. 16 A. J. Sober, Solar exposure in the etiology of cutaneous melanoma, Photodennatolo~, 4 (1987) 23-31. 17 B. W. Loggie and J. A. Eddy, Solar considerations in the development of cutaneous melanoma, Se&n. Chzcol., 15 (1988) 494-499.
Of what value is a highly absorbing photosensitizer
in PDT?
T. J. Dougherty and W. R. Potter Department of Radiation Medicine, RosweU Park Cancer Center, Elm and Carlton Streets, B@ii, IVY 14263-OOOI (U.S-4.j
An excellent recent review by Spikes [ 1] prompts us to emphasize a point previously made but perhaps not well appreciated regarding development of new photosensitizers for photodynamic therapy. In his article, Spikes states “HpD [haematoporphyrin derivative] absorbs poorly in the red region where tissue penetration by light is great. As a result, several other types of sensitizers have been examined that absorb more strongly and at longer wavelengths in the red, . . .“.
Iww!3ANDvIEws
Tanning with UVB or UVA: an appraisal of risks B. L. DifTey+ Regional Medical Ph@cs Departmenq Dryburn Hospital, Durham DHl STW (U.K.)
P. M. Farr Department of Dermatorosr/, Royal Victoria In@mary, Newcastle upon m WK.1
NEI 4LP
1. Introduction Prior to the mid-l 970s the only way of achieving a tan from an artificial source was to use a sunlamp. This was invariably an unfiltered medium or high pressure mercury arc lamp which emitted a broad spectrum of optical radiation from WC (200-290 nm) through to visible and IR radiation. Because of the high WC and WB (290-320 nm) emission, exposure times were short, typically a few minutes. These lamps were inefficient in tanning and it was not uncommon for overexposure to occur resulting in acute eye damage or skin erythema and blistering. Following the development of WA (320400 run) fluorescent lamps it became feasible to induce a tan with WA radiation. In the late 1970s and early 1980s it was suggested that a tan induced by WA was safer than that induced by WB. The tanning industry was quick to seize on this perceived benefit of WA and, as a consequence, WA lamps with minimal or no WI3 content were promoted. Whilst we do not condone tanning, we present arguments which indicate that those people who do wish to tan with arti.flcial sources may be better advised to use lamps in which the WB component, rather than the WA component, contributes the major fraction towards tanning. We consider four different types of lamp and discuss the biological and clinical consequences of tanning with lamps in which either WA or WI3 is the dominant wave band.
2. Lamp characteristics The lamps considered are a medium pressure mercury lamp, a type I WA lamp (e.g. Philips TL09), a type II WA lamp (e.g. Philips TLlO, Mutzhas WASUN) and a ‘simulated sunlight’ lamp. The latter lamp is one in which the ratio of WA to WI3 is similar to that in terrestrial sunlight and in which the W irradiance is such that the time required to achieve a minimal erythema is comparable with sunbathing in summer sunshine at mid-latitudes, i.e. +Author to whom correspondence
should be addressed.
220
NJZWSAND VIEWS
TABLE 1 Characteristics of different UV lamps used for tanning Lamp
Mercury arc sunlamp Simulated sunlight lamp Type I UVA lamp Type II UVA lamp
Radiation emission (%) 1 UVA UVB UVC
UVA
UVJ3
UVC
40 95 99 > 99.9
0 20 60 z-90
35 80 40
65 0 0 0
40 5 1
20 0 0 0
Contribution to tanning (96)
about 20 min. The radiation characteristics of the four lamps are summarized in Table 1. 3. Contribution
to tanning
By combining the spectral emission of each of the four lamps with the action spectrum for tanning it can be shown (Table 1) that the UVA and WB components of the lamps have a disproportionate effect on tanning. Since the action spectra for tanning and erythema are similar [ 11, we chose the Commission International de 1’Eclaire (CIE) reference erythema curve [2] in these calculations. Protagonists of UVA tanning have based their approach on the fact that there is a small divergence in the erythema and tanning action spectra at wavelengths longer than about 340 nm [ 31, indicating that it is possible to tan without burning, particularly for skin types III and above. These data have been extrapolated to imply that tanning with UVA is necessarily safer than with UVB, not only in terms of the risk of erythema, but also in respect of long-term effects such as skin cancer. There is little dispute that tanning with mercury lamps is ineffective and that users often end up with red rather than brown skin. However, in subjects who are able to tan well, both UVA sunbeds and natural sunlight (and presumably a ‘simulated sunlight’ lamp) are effective. The latter source, in which UVB is the dominant tanning wave band, has the additional advantage that epidermal hyperplasia develops providing increased endogenous photoprotection [ 41. 4. Risk of acute overexposure The common injuries from mercury arc sunlamp use are erythema and photokeratitis. Since the recommended exposure times with this type of lamp are only a few minutes, injuries most often occur when users fall asleep, neglect to use adequate eye protection or timers fail. With UVA sunbeds and suncanopies the exposure times required to induce a tan are around 30 min per session and so even exposure of up to 1 h is unlikely to result
NEWS AND VIEWS
221
in significant acute effects. Since the UV dose-erythema response characteristics of UVB and UVA radiation are very similar [5], a ‘simulated sunlight’ solarium, requiring exposure times of about 20 min to induce a tan, is likely to be equally safe in terms of erythema. 5. Clinical effects 5.1. Skin fragility and melunoc~tic lesions The widespread popularity of UVA stmbeds, particularly by users at home, has been accompanied by reports of increased skin fragility [6] and the induction of atypical melanocytic lesions [ 71. That these are new syndromes, previously unrecognized with either sunlight exposure alone or long-term exposure to the radiation from mercury arc sunlamps as occurs in psoriatic patients, suggests that the causative stimulus is high dose UVA radiation. 5.2. Photodermutoses The common photosensitivity disorder, polymorphic light eruption (PLE), often appears consequent to UVA sunbed use [8, 91. Although PLE is also induced by natural sunlight, there is good evidence that the precipitating radiation lies mainly in the UVA wave band [lo], and so it might be expected that the incidence of PLE would be higher as a result of tanning with UVA than with UVB. Support for this hypothesis is given by two studies. In one study [8] a sunbed incorporating type I UVA lamps was used and PLE occurred in 4 out of 33 subjects (12%). In a later study [9] using type II UVA lamps (i.e. much less UVEl than in type I UVA lamps), the incidence of PLE among the 31 subjects who took part was considerably higher (42%). Action spectra for photosensitivity caused by topical or systemic administration of drugs and chemicals are known to be principally within the UVA wave band. Consequently, tanning with high doses of UVA radiation is much more likely to result in a drug-induced photosensitive reaction in susceptible individuals than tanning with UVl3. 5.3. Photoaging Approximately one-third of the UVA radiation incident on white skin will penetrate to the dermis, compared with less than 10% of incident UVB. It is damage to dermal tissues which results in the features characteristic of photoaging: visible wrinkles, furrows and leatheriness. Although the relative importance of UVA and UVB for photoaging in human skin is unknown, there is evidence from animal experiments to suggest that tanning with UVA may result in a similar, or possibly greater, risk of photoaging than tanning with UVB [ll]. 5.4. Non-melanoma skin cancer We have no direct knowledge of the action spectrum for the induction of non-melanoma skin cancer in humans, although an action spectrum for
222
NEWSANDVIEW8
photocarcinogenesis in mouse skin has been determined recently (121. The correspondence of this action spectrum and that for tanning in humans [ 1, 31 is close, particularly when allowance is made for the different optics of mouse and human skin [ 131. This similarity has led others to the conclusion that tanning with either UVB or UVA results in risks of non-melanoma skin cancer of a similar order of magnitude [ 131. In other words, the idea that tanning with UVA is safer than with UVB, in terms of non-melanoma skin cancer risk, can no longer be sustained [ 141. 5.5. Melanoma
The use of artificial tanning equipment has been shown to be a weak risk factor in the induction of cutaneous melanoma [ 151. The relationships between melanoma and sunlight exposure are complex, and the action spectrum for the induction of melanoma by UVR is unknown. Although UVE? radiation is considered by some [ 16} to be the wave band primarily responsible, the possibility that the action spectrum for melanoma lies within the UVA, visible or even the near-IR parts of the solar spectrum cannot be discounted [ 171. For this reason it would be unwise to compare the relative risks of tanning with either UVEIor UVA in respect of melanoma. 6. Discussion Exposing the skin to any combination of UV wavelengths is not without risk to health, particularly in those subjects who do not tan or tan poorly. This view is widely held by skin specialists but, despite consequent warnings, a signiflcant number of people are continuing to use artificial sources to acquire a tan that is perceived to be socially desirable. The vast majority are doing so using appliances in which the effective radiation lies mainly or wholly within the UVA wave band. The general acknowledgement that tanning with UVA is safer than with WI3 is reflected in the regulations and advice concerning the manufacture and design of sunbeds given by many national regulatory authorities and consumer groups. On the basis of the arguments presented above, we question this wisdom and suggest that a course of sunbed sessions, undertaken with the intention of tanning, may be achieved with less risk of adverse effects if the lamps used have an emission spectrum in which the effective radiation lies principally in the UVB, rather than the UVA, wave band, like that of terrestrial sunlight.
1 J. A. Parrish, K. F. Jaenicke and R. R. Anderson, Erythema and melanogenesis action spectra of normal human skin, Photo&em. Photobid., 36 (1981) 187-191. 2 A. F. McKinlay and B. L. Diffey,A reference action spectrum for ultraviolet induced erythema in human skin, CIE J., 6 (1987) 17-22. 3 R. W. Gange, Y. K. Park, M. Auletta, NKagetsu, A. D. Blacken and J. A. Parrish, Action spectra for cutaneous responses to ultraviolet radiation, in F. Urbach and R. W. Gange (eds.), The Biological Effects of WA Radiation, Praeger, New York, 1986, pp. 57-85.
NEWSANDVIEWS
223
4 R. W. Gsnge, A. D. Blackett, E. A. Matzinger, B. M. Sutherland and I. E. Kochevar, Comparative protection efficiency of UVA and WB-induced tans against erythema and formation of endonuclease-sensitivesites in DNA by UVB in humanskin,J. Invest. DennatoL, 85 (1985) 362-364. 5 B. L. Diffey, P. M. Farr and A. M. Oakley, Quantitative studies on UVA-induced erythema in human skin, Br. J. DermaioL, I17 (1987) 67-66. 6 P. M. Farr, J. M. Marks, B. L. Diffey and P. Ince, Skin fragility and blistering due to use of sunbeds, Br. Med. J., 296 (1988) 1708-1709. 7 S. K. Jones, H. Moseley and R. M. MacKie, WA-induced melsnocytic lesions, Br. J. DermutoL, I17 (1987) 111-115. 8 M. S. Devgun, B. E. Johnson and C. R. Paterson, Tanning, protection against sunburnand vitamin D formation with a W-A ‘sunbed’, Br. J. DermuZoL, I07 (1982) 275-284. 9 J. K. Rivers, P. G. Norris, G. M. Murphy, A. C. Chu, G. MidgIey et uI., UVA sunbeds: tanning,photoprotection, acute adverse effects and immunologicaIchanges& J. DermatoL, I20 (1989) 767-777. 10 P. M. Farr and B. L. Diffey, Adverse effects of sunscreens in photosensitive subjects, Lancet, i (1989) 429-431. 11 D. L. Bissett, D. P. Hannon and T. V. Orr, Wavelength dependence of histologicaL physical and visible changes in chronicalIy W-irradiated hairlessmouse skin,Photo&em. PhotobioL, 50 (1989) 763-769. 12 H. J. C. M. Sterenborg, Investigations on the action spectrum of tumorigenesisby ultraviolet radiation, Ph.D. Thesis, Utrecht, 1987. 13 L. Roza, R. A. Baan, J. C. van der Leun and L. Kligman, UVA hazards in skin associated with the use of tanning equipment, J. Photochem PhotobioL B: BioL, 3 (1989) 281-287. 14 H. J. C. M. Sterenborg and J. C. van der Leun, Tumorigenesis by a long wavelength UVA source, Photo&em. Photobiol., (1990) 325-330. 15 A. J. Swerdiow, J. S. C. English, R. M. Ma&e, C. J. O’Doherty, J. A. A. Hunter et al., Fluorescent lights, ultraviolet lamps, and risk of cutaneous melanoma, Br. Med. J., 297 (1988) 647-650. 16 A. J. Sober, Solar exposure in the etiology of cutaneous melanoma, Photodennatolo~, 4 (1987) 23-31. 17 B. W. Loggie and J. A. Eddy, Solar considerations in the development of cutaneous melanoma, Se&n. Chzcol., 15 (1988) 494-499.
Of what value is a highly absorbing photosensitizer
in PDT?
T. J. Dougherty and W. R. Potter Department of Radiation Medicine, RosweU Park Cancer Center, Elm and Carlton Streets, B@ii, IVY 14263-OOOI (U.S-4.j
An excellent recent review by Spikes [ 1] prompts us to emphasize a point previously made but perhaps not well appreciated regarding development of new photosensitizers for photodynamic therapy. In his article, Spikes states “HpD [haematoporphyrin derivative] absorbs poorly in the red region where tissue penetration by light is great. As a result, several other types of sensitizers have been examined that absorb more strongly and at longer wavelengths in the red, . . .“.