Re: Sunscreen use, wearing clothes, and number of nevi in 6- to 7-year-old European children.

In a recent report, Autier et al. described the correlation of nevi development with sunscreen use in children (1). This apparently counterintuitive finding will be the source of extensive discussion and perhaps some controversy. However, when the dynamics of skin biology are considered, it is important to recognize this study for what it really tells us. Specifically, it reminds us just how ignorant we are of all the complexities of skin biology and the impact of solar radiation. We are comfortable with the fact that the exposure of skin to sunlight causes sunburn and the unquestionable value of sunscreens for the prevention of sunburn (2). While it is tempting to extrapolate the protective effects of sunscreens to the prevention of skin cancers as well, it is important to recognize that the wavelengths (action spectra) that cause the effect on skin (sunburn) and those wavelengths that cause the induction of different types of skin cancer may be different. While good data exist that implicate sunburn-causing wavelengths of solar radiation in the development of squamous cell carcinoma, much less convincing evidence exists for the development of basal cell carcinoma and malignant melanoma in humans. Protective clothing and sun avoidance drastically alter the effects of all wavelengths of sunlight on the skin. On the other hand, sunscreens are not impervious barriers to sunlight. Depending on the specific formulation, various wavelengths can be transmitted to underlying skin cells. A UVB (ultraviolet B)-blocking sunscreen, very effective at preventing sunburn, will permit the transmission of UVA (ultraviolet A) radiation. Even products claiming UVA protection will allow the penetration of varying amounts of UVA. While the ability of UVA radiation to directly damage DNA is far less than that of UVB, recent data suggest that energy