Melanoma is not caused by sunlight.

When comparisons are made of cutaneous melanoma with cutaneous squamous cell cancer (SCC) and basal cell cancer (BCC) of the skin with respect to age dependence, sex ratio, distribution on the body, association with sun exposure, and variation with latitude, it is clear that SCC is due almost entirely to sun exposure, that BCC is partly due to sun exposure, and that melanoma is not due to sun exposure. For melanoma, it is only latitudinal variation that favours the hypothesis of sun exposure causation. However, an examination of the latitudinal variation of SCC incidence reveals that this is several fold greater than can be accounted for by variation of exposure to UV-B. The other factor operating appears to be skin temperature. For melanoma, it is postulated that the latter factor by itself may suffice to account for the observed variation with latitude. The higher incidence of melanoma in the higher social classes and its increasing incidence with age may be readily explained by the hypothesis that melanoma incidence increases with increase in skin temperature.