Decreased p53 expression in chronically sun-exposed human skin after topical photoprotection

W-induced DNA damage appears to play an essential role in skin carcinogenesis. Following acute UV irradiation, there is an overexpression of normal p53 protein in epidermal keratinocytes, representing a physiological response to DNA damage. Sun protection through topical sunscreens or clothing is believed to reduce the hazardous effects of UV irradiation and subsequently the risk of skin cancer. We have examined the effect of an SPF 15 topical sunscreen and blue denim fabric (SPF 1700) in chronically sun-exposed human skin after sun exposure during a normal summer. Skin biopsies from sun-protected and sun-exposed skin were compared with respect to immunohistochemically detectable p53. This method provides a model for assessing the significance of different degrees of UV protection under physiological conditions. Our results show a significant reduction of p53-positive cells in sun-protected skin as compared with sun-exposed skin. The reduction of p53-positive keratinocytes differed between topical sunscreen (33% reduction) and blue denim fabric (66% reduction). Interindividual variations were large, possibly because of variations in sun exposure. These variations also suggest that mechanisms determining UV damage at the cellular level are complex. The role of residual p53-positive keratinocytes after 2 months of total sun-protection (i.e., SPF 1700) is discussed.