Re: Sunscreen use and duration of sun exposure: a double-blind, randomized trial.

Autier et al. (1) reported that sun-screen use seems to encourage longer recreational exposure to the sun. We wish to supplement their results with data on the effects of sunscreens and tanning on ultraviolet (UV)-induced DNA damage in human skin. Our data have become available through a recently developed method for measuring UV-induced DNA damage, i.e., cy-clobutane pyrimidine dimers and pyrim-idine (6-4) pyrimidone photoproducts, in human skin biopsy specimens (2–4). We used this method to test the effects of sunscreens on human skin in situ (2). Sunscreen was applied by one person, according to the manufacturer's instructions. While protection against the ery-themal response varied fivefold among nine subjects, protection against DNA damage differed by a factor of 10 and was independent of the erythemal response. On average, sunscreen protected users against DNA damage in accordance with the sun protection factor (SPF), but the protection was highly individual. Since SPF is based on average erythemal response, it is no guarantee against individual DNA damage. Tanning provides an endogenous " sunscreen " with an SPF of 3–5 (5). These measurements are based on protection against erythema, and, to our knowledge, fundamental data on how well tanning protects genetic material are lacking. In unpublished studies, simulating the use of sunbeds, we investigated the effects of tanning on DNA damage in situ. We measured the protective effects of tanning by quantifying the levels of UV-induced photoproducts in the skin of eight healthy, fair-skinned Caucasians. The study was approved by the South Stockholm Ethical Review Board, which serves both institutions involved in the work, and subjects gave written informed consent to participate. Each subject was irradiated on a 2 × 4-cm area of skin on the lower back with ultraviolet B (UVB) at a dose of 0.3 J/cm 2 and on a second 2 × 4-cm area with a dose of 0.6 J/cm 2. A punch biopsy was performed immediately after irradiation. An additional biopsy was performed on unirradiated skin to provide a background control specimen. Next, tanning was induced by 10–13 sessions of UVA irradiation for 3 weeks. Tanning was observed by a clear change in skin color toward brown and measured with a reflectometer adjusted to record melanin pigmentation. In the course of ultraviolet A (UVA) treatment , the instrumental readings indicated an increase in pigmentation of 38.8 ± 16.7 reflectometer units (mean ± standard deviation [SD], n ‫ס‬ 8). After the last …