Letter to the editor Lack of sunbed-induced skin changes due to insufficient UV exposure Robert M. Sayre 1,2 , John C. Dowdy 1 1 Rapid Precision Testing Laboratories, Cordova, TN 38016, USA, and 2 Department of Medicine, Division of Dermatology, University of Tennessee, Center for the Health Sciences, Memphis, TN 38163, USA To the Editor, Ruegemer et al. (1) recently reported a large study of the exposure consequences of indoor tanning in 99 skin type II and III individuals. After 6 weeks of twice weekly exposure the authors reported clinically obvious tanning and no erythema using both visual and objective coloro- metric measurements, while tabulating results showing changes of questionable significance. They also report no significant changes in surface urocanic acid, no changes in UV sensitivity because of tanning, and no epidermal hyperplasia from histological examination of biopsies. Exposures had been administered using a commercial tanning unit with 0.9% UVB. Two dosage levels were reported in which one group received 1.13 J/cm 2 and the other 1.46 J/cm 2 each session twice weekly for 6 weeks. This equates to a total dose for the 6 weeks exposure series of 13.6 and 17.5 J/cm 2 , respectively. For the two irradiation times and the two delivered doses of 1.13 and 1.46 J/cm 2 , the irradiance must have been 2.7 mW/cm 2 or 27W/m 2 and not `irradiance 0.27 W/m 2 ' as stated by Ruegemer et al. (1). An irradi- ance of 2.7 mW/cm 2 is low for today's tanning units. The authors did not report any spectral or radiometric methods upon which they base their dosimetry. The reported doses received by the subjects were not object- ively documented. The irradiance and dosage discrep- ancy needs to be resolved. If one assumes that sunlight has 4mW/cm 2 UV, then the 1.46 J/cm 2 dose is achieved in approximately 6 min. It is difficult to believe that 6min of sunlight exposure twice weekly for 6 weeks could produce statistically significant changes in skin color, UCA isomer levels, epidermal thickness, or UV sensitivity. It is our understanding that European rules require that bulbs used in indoor tanning units must be suitable for a 30-min exposure session, the shortest timer allowed on such devices (2, 1995 #61). Certainly 3 times weekly and possibly 5 or even 7 times weekly exposures are not unacceptable (2, 1995 #720). If this is the case, then the subsequent discussion of exposure risk based upon the non-results reported and exposures administered can hardly be justified. In this Journal, Caswell (3) reported such a study not referenced by Ruegemer et al. (1). Caswell reported that statistically significant levels of tanning occurred based upon Chromometer measurement and graded visual as- sessment. Ruegemer et al. (1) claim to have observed `clinically obvious' tanning but do not statistically dem- onstrate this with their Chromometer measurements. Analysis of Ruegemer et al.'s results (Table 1, p. 224) shows that the tanning parameter DE reported by Cas- well varied by an average of 3 units. Caswell reported a three-unit variation of DE for his non-irradiated sites changing during entire study. Surely, Rugemer's three- unitvariationcannotrepresentclinicallyobvioustanning andassuchwouldnotbeexpectedtoalterUVsensitivity. While Caswell reports data collected for 8 weeks and not 6 weeks, he provided an exposure schedule for the entire study. Taking the first 12 exposures accomplished in 4 3weeks, Caswell's Skin type III group received 135 min exposure and his skin type IV group 159 min. The tanning bed used by Caswell had a UV irradiance of 17.5 mW/cm 2 . The accumulated exposure for Cas- well's Skin Type III group was 143 J/cm 2 and for the Skin Type IV group 167 J/cm 2 . Caswell reports a DE at the 13th visit of 6.53 + 3.93. With this exposure regimen, objective visually graded tans have already occurred. 39 Photodermatol Photoimmunol Photomed 2003; 19: 39±40 Blackwell Munksgaard Copyright ß Blackwell Munksgaard 2003 Photodermatology Photoimmunology & Photomedicine ISSN 0905-4383