Abstract
Direct quantitative comparison cannot be drawn between experimental induction of cancer in laboratory animals with ultraviolet light and the hazard of skin cancer in man resulting from this agent. Reasons for this are: (1) the very different optics in the two cases, ultraviolet light penetrating to deeper tissues in mice than in man and hence producing different types of cancer; (2) quantitatively indeterminable biologic differences between man and experimental animals; (3) the fact that reliable statistics permitting comparison of incidence of skin cancer with incidence of exposure to ultraviolet B of sunlight are sparse and difficult to obtain. The cumulative carcinogenic effect of repeated doses, clearly shown in animal experiments, makes it important to consider this hazard in terms of repeated exposure, whether to sunlight or to artificial sources of ultraviolet light or to a combination of both, rather than in terms of the magnitude of single doses.