Affiliations of authors: F. P. Gasparro, Department of Dermatology, Thomas Jefferson University, Philadelphia, PA; M. Berwick, Department of Epidemiology, Memorial Sloan-Kettering Cancer Center, New York, NY.
Correspondence to: Francis P. Gasparro, Ph.D., Department of Dermatology, Thomas Jefferson University, 233 South 10th St. (BLSB 428), Philadelphia, PA 19107 (e-mail: francis.gasparro{at}mail.tju.edu).
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 from these wavelengths (and those in the shorter portion of the visible spectrum) can be absorbed by endogenous photosensitizers and oxidize DNA bases (3). Since the technology to detect these latter effects has only been developed recently, it is too early to know the effect of sun exposure on human skin cells. The foregoing explanation thus highlights the extent of our ignorance concerning skin biology and the effects of solar radiation.
To begin to address this area, we need detailed studies of action spectra to elucidate the wavelength dependence for the following: 1) DNA damage, 2) immune suppression, and 3) genes that control important related activities, such as DNA repair and cell-cycle progression. Only then will we be able to design appropriate, preventive strategies for effects other than sunburn. An obvious question raised by Autier et al. is "Which wavelengths are responsible for nevi development?"
These questions can be answered by carefully designed photobiology experiments. In 1989 and 1998, the National Institutes of Health sponsored conferences on solar radiation and skin. After participating in the 1998 conference and reading the report on the 1989 conference, we thought that it is striking how similar the questions were a decade later. We have the tools to perform these experiments. We have the molecular biology insight to ask the right questions. What is needed is the following: 1) the desire to know this information, 2) the resources to conduct these experiments, and 3) the establishment of a consensus among the researchers, the Food and Drug Administration, funding sources, and industry that these experiments are important. In an era of "healthy people," it would be expected that the number one environmental agent that affects human biology would have the highest priority for research.
REFERENCES
1
Autier P, Dore JF, Cattaruzza MS, Renard F, Luther H,
Gentiloni-Silverj F, Zantedeschi E, et al. Sunscreen use, wearing clothes, and number of nevi in
6- to 7-year-old European children. J Natl Cancer Inst 1998;90:1873-80.
2 Gasparro FP, Mitchnick M, Nash JF. A review of sunscreen safety and efficacy. Photochem Photobiol 1998;68:243-56.[Medline]
3 Pflaum M, Kielbassa C, Garmyn M, Epe B. Oxidative DNA damage induced by visible light in mammalian cells: extent, inhibition by antioxidants and genotoxic effects. Mutat Res 1998;408:137-46.[Medline]
![]() |
||||
|
Oxford University Press Privacy Policy and Legal Statement |