All UV exposure causes DNA damage and induces other potentially carcinogenic molecular and cellular lesions. Hence, UV tanning represents an avoidable risk factor for melanoma and nonmelanoma skin cancer (21
) and the FDA discourages this practice (http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm186687.htm
). Our previous studies (9
) showed that repeated UV exposures produce significant DNA damage. Interestingly, the levels of cyclobutane pyrmidine dimers decreased while the numbers of p53-positive cells increased as the cumulative dose of UV increased. These measurements were taken at the end of the exposure series and compared with an unexposed control site. It would be useful to assess UV damage at multiple times during the course of the repeated exposures. Such data would help to fully assess the differences in UV damage caused by different exposure protocols.
There are at least two approaches that can be used to reduce the cumulative dose to UV tanners: (1) reduce the frequency of exposures and/or (2) reduce the absolute dose per exposure. Because it is well-known that a tan takes up to 5 days to develop (5
), we chose to reduce the frequency of exposure to two times per week. In addition, de Winter et al
) showed that it takes 3 to 4 days for DNA damage from a 1.2 individual MED dose to return to background levels. Dowdy et al
) propose a universal indoor tanning exposure schedule, based on 3 exposures per week; but using a maximum dose of 500 J/m2
, instead of the 600 J/m2
used in our study. Even with the reduced maximum dose, their cumulative dose over a 4-week time period is 20% higher than that resulting from our exposure protocol B. Our previous publication (9
) showed that exposure protocol B produced similar pigmentation to protocol C, which used a 46% higher cumulative dose. Thus, merely reducing the maximum allowable dose does not achieve the same savings in cumulative dose as does reducing the frequency of exposure. Nevertheless, any means of reducing the UV burden should be explored and, in fact, our studies (9
) have shown that the cumulative dose required to produce a moderate tan can be reduced by a factor of 2 to 3 below the doses used in current practices. The fact that higher skin phototypes can tan as well, or better, than lower phototypes (5
) prompted us to study the differences in pigmentation caused by repeated UV exposures in humans of different phototypes.
To our knowledge, this is the first study that compares resulting pigmentation levels when different skin phototypes are given identical repeated, physical doses. As early as 1983, Pathak and Fanselow found similar MMDs for skin phototypes 2 to 4. Since that time, most studies of UV-induced pigmentation in different skin phototypes have used doses that increased according to skin phototype. In 2000, Caswell (25
) exposed phototype 3 and 4 subjects to UV radiation from tanning beds using the 1986 FDA guidelines. He administered three exposures per week over a period of eight weeks. Slight adjustments were made to the exposure time for different skin phototypes, resulting in a cumulative dose of 92.4 SED (9240 J/m2
-eryth. eff.) for phototype 3 and 94.4 SED (9440 J/m2
– eryth. eff.) for phototype 4. However, he saw no significant differences in tanning response of phototypes 3 and 4 (26
). Sheehan et al
) saw higher levels of tanning in skin phototype 4 compared to phototype 2, when daily, equally erythemogenic doses of 0.65 MED (pre-determined for each individual) were administered. The physical doses given to phototype 4 were approximately 30% higher than those given to phototype 2 subjects.
Ravnbak and Wulf (28
) exposed skin phototypes 2 to 5 to four different UV sources. Their exposure protocol was based on the individual MMD, which was 5.3 SEDs for phototype 2 and 10.5 SEDs for phototype 5, with intermediate values for phototypes 3 and 4. After five daily repeated exposures, they found that the MMD was independent of pre-exposure pigmentation and skin phototype, except when a solar simulator and narrow-band UVB sources were used. Their study provides useful supplementary data on skin phototypes 4 and 5 that supports our findings on skin phototypes 2 and 3.
To categorize the UV sensitivity of the study subjects, we used the classic Fitzpatrick Phototyping system and the industry-developed NTTI system. Our results did not find any statistically significant relationship between Fitzpatrick phototype and the MED or MMD. This has been reported by others (29
). Regardless of the phototyping approach, our final results were very similar. It is interesting to note that there were more subjects who were categorized as phototype 3 using the NTTI system than there were when using the Fitzpatrick system (31 vs 13). This indicates that the NTTI system is more liberal in assigning skin phototype than the classic Fitzpatrick system.
In summary, using different analyses, we showed that the propensity of phototype 3 to develop UV-induced pigmentation is the same or greater than phototype 2, when identical exposure schedules are administered. Hence, there is no reason to differentiate guidance on developing a tan for different phototypes. This indicates that the FDA Guidance of 1986 (4
) should be revised – not only by allowing the use of a universal schedule for all phototypes - but also to decrease the frequency of exposure and, thereby, reduce the cumulative dose (24
). The use of our phototype-independent schedules can substantially reduce the UV burden to those who, in spite of medical advice and educational efforts, use UV for intentional tanning and, in particular, for skin phototypes 3 to 5.