Childhood sun exposure as a risk factor for melanoma: a systematic review of epidemiologic studies

Objective: To review the evidence that childhood is a period of particular susceptibility to the carcinogenic effects of solar radiation. Methods: Studies were identified through searches of computerized bibliographic databases and article reference lists. Eligible studies were those that reported risks of melanoma associated with sun exposure during two or more age-periods. Results: The measurement of childhood sun exposure varied across studies, preventing formal meta-analysis for most measures. We found that the way in which sun exposure was measured led to strikingly different conclusions regarding the association between age-specific sun exposure and risk of melanoma. Ecological studies assessing ambient sun exposure consistently reported lower risks of melanoma among people who resided in a low ultraviolet (UV) environment in childhood compared with those who resided in a high UV environment. In contrast, case-control studies differed widely in their findings, and no consistent associations with childhood sun exposure were observed. Conclusions: Ecological studies provided better-quality evidence than case-control studies for examining the effects of exposure to sunlight during specific age periods. Exposure to high levels of sunlight in childhood is a strong determinant of melanoma risk, but sun exposure in adulthood also plays a role.