| The incidence of skin cancer, particularly the fatal malignant melanoma, is rapidly increasing in white skin populations throughout the world. In the past decade, controversy has arisen over the use of sunscreens in the prevention of skin cancer induced by sun. In this thesis project an extensive review of epidemiologic studies and analysis of gene mutations indicate that sun exposure may be the key risk factor in the onset of non-melanoma skin cancer as well as melanoma.; In this thesis project, the possible role of sunscreen in prevention of sun-induced DNA damages was examined. The ability of daily applications of sunscreen with a protection factor (SPF) of 15 to prevent UV-induced DNA damage (cyclobutane thymine dimers) was investigated. A total of 24 female subjects were enrolled with appropriate Institutional Review Board approval. Daily sunscreen SPF 15 was applied over one of five delineated areas on the buttock. Another area served as control (unirradiated). To simulate intermittent sunscreen use, an SPF 15 product was applied to the remaining sites on 3 of 4 days, with one missed application on days 2, 3, or 4. After a period of 30 min, the center of each site was irradiated with 2 MED (290–400 nm) for 4 consecutive days. Twenty-four hours after the last irradiation biopsy specimens were obtained from the exposed treated and the unirradiated control sites. Dimers were assayed in skin sections by immunohistochemistry using a monoclonal antibody against thymine dimers. The epidermal area was measured by computer image analysis and the number of antibody-positive cells per mm 2 of epidermis was determined. There was no statistically significant difference in the number of positive nuclei between unirradiated skin and irradiated skin on which sunscreen was applied daily. In contrast, there was a statistically significant difference in thymine dimer formation between the former two groups and the groups in which sunscreen application was skipped 24, 48, and 72 hours prior to obtaining the biopsy. |
