Criticism of FDA pilot study unfounded (response to R. M. Sayre and J. C. Dowdy)

To the Editor, We appreciate the opportunity to respond to R. M. Sayre’s and J. C. Dowdy’s correspondence [Sayre and Dowdy (1)] regarding our pilot study on indoor tanning exposure schedules (2). Sayre and Dowdy analyzed our data and indicated that our study is ‘flawed’ because we relied on statements provided by Caswell and colleagues (3, 4) that their study ‘followed FDA guidelines for tanning bed exposures’. Sayre and Dowdy now claim that the exposure schedules used in Caswell’s study deviated from current FDA guidelines. To verify this assertion, we contacted Dr. Michael Caswell. According to Dr. Caswell, their sunbed output was re-measured during the study and a new maximum exposure time was calculated. They determined that during weeks 4 and 5, the doses were 10% below the maximum allowable dose. Therefore, Drs. Caswell and Sayre opted to increase the exposure time to 25min for weeks 6–8. This resulted in a dose that was 10% higher (not 25% as Sayre and Dowdy claim) than the theoretical maximum during weeks 6–8. Caswell believes that this change did not significantly affect the biological response and we agree. Using this information, our calculations indicate that the cumulative dose used in the Caswell study was approximately 2% higher than that recommended by the current FDA guidelines (5). This small difference is highly unlikely to have any impact on the important findings of our pilot study, i.e. that we were able to produce similar tans to those achieved following current guidelines by using cumulative doses that were at least a factor of three lower. Sayre and Dowdy also point out that we did not determine the degree of ‘erythemic UV acclimatization’ maintained by once or twice a month exposures. This is correct, and nowhere in our study do we claim that ‘erythemic acclimatization’ achieved with our study is equivalent to that which may be obtained with the current FDA guidelines. Also, based on current literature (6, 7) the degree of erythemic acclimatization conferred by a sunlamp-induced tan is small, equivalent to a ‘sun protection factor’ of 1.7–4. Sayre and Dowdy also state that the 6 SED maximum exposure used in our study is approximately 30–60% larger than the current maximum dose allowed by the FDA policy. Based on our calculations, the maximum dose used in our pilot study was 35–45% higher than the maximum dose allowed by the FDA policy. This difference results from the fact that we used the internationally-accepted CIE erythemal action spectrum, which varies from the CIELytle action spectrum published in the 1986 FDA Policy Letter. In designing our study, we chose a maximum dose of 600 J/m–CIE (6 SED) as being approximately equivalent to the maximum dose in the FDA Policy Letter of 624 J/m–FDA. As Sayre and Dowdy note, this dose is highly dependent on the emission spectrum of the sunlamp. Based on our earlier study (8), the ratio of 6 SED to 4 MED–FDA as currently defined by the FDA ranged from 1.10 to 1.48 for six different types of sunlamps which were evaluated. Again, this difference in maximum dose has no effect on the conclusions presented in our paper. The objection of Sayre and Dowdy that we only studied the lower back area of our subjects, and that the tanning response may be different on different parts of the body, also has absolutely no bearing on the conclusions of our study. We place in the same category an objection to our using trained observers and color-measuring instrumentation for evaluation of skin color changes. Our approach optimizes information by combining subjective evaluation by an investigator with objective quantitative measurement. Sayre and Dowdy assert that an adequate evaluation of whether a tan has reached the optimal level can only be made by the individual who is seeking the tan. This might be an interesting study of ‘customer satisfaction’ rather than a photobiologic exploration of the tanning process. The data from our Photodermatol Photoimmunol Photomed 2007; 23: 59–60 Blackwell Munksgaard r 2007 The Authors. Journal compilationr 2007 Blackwell Munksgaard