Sharon A. Miller

Humans have been exposed to solar UV radiation since their appearance on Earth and evolution has enabled most individuals to adapt to this exposure, to some degree. UV radiation produces several deleterious effects in human skin and light-skinned individuals are at greatest risk for both acute and long-term negative effects such as DNA damage, sunburn, immune suppression and skin cancer. The benefits of photoadaptation, which leads to a decreased response after acclimatization, are that humans who have skin that is capable of photoadaptation can work and play in the sun with reduced fear of painful sunburn. However, the effects of photoadaptation on DNA damage and development of skin cancer are quite complex and less well-understood. In this article, we have reviewed the current state of knowledge of UVR photoadaptation in human skin. However, more studies are needed to explore the use of UVR photoadaptation to protect against critical endpoints, such as skin cancer.

Erythema (i.e. visible redness) and DNA damage caused by ultraviolet radiation (UVR) in human skin have similar action spectra and show good correlation after a single exposure to UVR. We explored the potential to use instrumental assessments of erythema as a surrogate for DNA damage after repeated exposures to UVR. We exposed 40 human subjects to three different exposure schedules using two different UVR sources. Cyclobutane-pyrimidine dimers (CPDs) in skin biopsies were measured by immunofluorescence, and erythema was assessed by both the Erythemal Index (EI) and the Oxy-hemoglobin (Oxy-Hb) content. Surprisingly, the skin with the highest cumulative dose ended up with the lowest level of DNA damage, and with the least erythema, as assessed by Oxy-Hb (but not EI) 24 h after the last UV exposure. Although the level of CPDs, on average, paralleled Oxy-Hb (R² = 0.80–0.94, P = 0.03–0.11), the correlation did not hold for the pooled individual measurements (R² = 0.009, P = 0.37) due to potential individual differences in UV-induced photoadaptation. We suggest that the methodology may be optimized to improve the correlation between DNA damage level and erythema to enable noninvasive risk assessment based on erythema/Oxy-Hb content for individual human subjects.

There have been many recent reports regarding the potential risks of UV emissions from compact fluorescent lamps (CFLs). In some of these reports, the robustness of the measurements was difficult to discern. We conducted round-robin measurements, involving three lamp manufacturers and two government research laboratories to gather reliable data on the UV emissions from commercially-available CFLs. The initial sample of lamps consisted of 71 spiral-shaped CFLs purchased from local retailers. From the initial sample, 14 ‘high UV emitting’ CFLs were chosen for further evaluation. We compared the UV emissions at a distance of 20 cm with the UV exposure limits (ELs) published by the International Commission on Non-ionizing Radiation Protection (ICNIRP). We found that the allowable exposure time for measured lamps ranged from 21 to 415 hrs. This indicates that the emissions would not exceed the short-term ELs that have been established by the ICNIRP for healthy individuals. We also evaluated the potential long-term risk and found it to be insignificant. There was a large variation in the UV emissions found, even for lamps from a single package, indicating that it is impossible to predict the UV output of a CFL based on its physical appearance and model designation.

Summary: Background: The Food and Drug Administration has published guidelines for manufacturer‐recommended exposure schedules for ultraviolet (UV) tanning, intended to limit acute and delayed damage from UV exposure. These guidelines recommend that exposure schedules be adjusted for skin phototype. However, it has been shown that the dose necessary to produce tanning is similar for phototypes 2–4.Methods: We observed tanning in phototypes 2 and 3 from repeated UV exposures over a 5‐week period. Pigmentation was evaluated visually, instrumentally, and through Fontana‐Masson staining of biopsies.Results: The resultant pigmentation was equal or greater in phototype 3 compared with phototype 2 – both visually and instrumentally – measured on day 31 of the exposure protocol. The amount of melanin measured in biopsies taken 24 h postexposure was also greater in phototype 3 compared with phototype 2.Conclusion: Published data on tanning in phototypes 4 and 5 support our findings that higher phototypes can develop pigmentation more efficiently than lower phototypes. Therefore, a universal exposure schedule (based on sensitivity of phototype 2) can be used for all phototypes that are expected to engage in indoor tanning. This approach will result in a reduction of the UV burden for skin phototypes 3 and above.

Cutaneous transilluminators are light-emitting devices used to localize blood vessels for various medical procedures. They are often used in populations that may be at increased risk for skin burns, such as neonates and the elderly. While there is a known potential for skin burns, little is known about the ophthalmic risk from the use of these devices. This paper will report on the laboratory evaluation of the potential ocular hazards from transilluminators (TIs). Our results indicate that transilluminators which incorporate white-light LEDs have emissions that have the potential for producing injury to the retina, especially in patients who may have a reduced aversion response.

Background The dynamics of ultraviolet (UV)-induced melanogenesis have been well characterized for single UV exposures. However, our knowledge of the effects of repeated UV exposures on the development of new pigmentation is limited. Objectives To characterize the dynamics and dose dependence of pigmentation induction by repeated UV exposures using two different UV sources. Methods A total of 40 healthy subjects participated in the study: 21 were exposed to a 5% UVB/95% UVA source and 19 were exposed to a 2% UVB/98% UVA source. Skin phototypes 2–3 were represented. Subjects were exposed one to three times per week. The minimal erythemal dose and minimal melanogenic dose of all subjects were determined, and both visual and instrumental observations of the development of pigmentation and erythema were recorded. Results Dark-brown pigmentation could be produced by a cumulative UV dose of 4200 J m⁻² given as 10 exposures over 5 weeks. However, comparable pigmentation could also be induced by a cumulative dose of 2900 J m⁻² given as eight exposures over 4 weeks. The lowest cumulative dose of 1900 J m⁻² given over 4 weeks produced moderate pigmentation. The 2% UVB source led to earlier and darker pigmentation than the 5% UVB source did for equally erythemogenic doses. Conclusions These observations show that the dynamics of melanogenesis induced by repeated exposures depends on UV dose, dose interval and emission spectrum. They also indicate that increasing the UV dose above a certain level of cumulative exposure does not significantly increase the level of UV-induced pigmentation.

The development of new pigmentation (tan) in human skin after UV exposure requires several days. Once it is developed, the tan can last for weeks. Current recommendations for tanning exposure schedules in the USA (FDA Letter to Manufacturers: Policy on maximum timer interval and exposure schedule for sunlamps, August 21, 1986) allow exposures three times per week for the development of a tan, and one to two times per week for maintenance exposures. However, this policy is often interpreted in the indoor tanning industry as allowing three exposures per week on a continuous basis. We believe that the reduction of the recommended cumulative dose to indoor tanners should be explored. Two approaches for achieving this are (1) decreasing the number of exposures and (2) increasing the time interval between exposures. To explore such changes, we conducted a pilot study. The pilot study involved three exposure schedules (evaluated on each of six subjects) that evolved throughout the course of the study. Digital photography, visual assessment and diffuse reflectance spectrometry were used to assess skin color changes. The six pilot subjects were studied for 8-18 weeks. The changes in skin color obtained through the use of the different exposure schedules were compared with changes reported by Caswell (Caswell M, The kinetics of the tanning response to tanning bed exposures, Photodermatol Photoimmunol Photomed 2000: 16: 10-14) who used schedules based on current recommendations. Two out of the three experimental schedules produced tans comparable with those reported by Caswell. In these two schedules, cumulative doses were a factor of 2-3 below doses from current schedules. The UV burden to indoor tanners can be substantially reduced without compromising the cosmetic effect. These results need to be confirmed in a larger study.