With enough exposure, even a dark-skinned subject who rarely burns is at a substantial risk for nonmelanomatus carcinoma 2 . It takes several years, however, for the effects of solar exposure to become evident. Thus, sun avoidance and protection are most important in early years. UVB Exposure A number of exogenous and endogenous factors work interactively to increase or decrease UVB exposure. Skin type also has a significant effect on the risk of sun burn and the rate of cutaneous synthesis of vitamin D 3 .
Skin is pigmented by melanin which acts as a natural sunscreen.
Fair skinned individuals, for example, have been shown to produce six times more vitamin D than dark skinned people exposed to similar UVB levels. Sunscreens block the absorption of UV-B which is the same radiation required for cutaneous synthesis of vitamin D 5 . Barrier sunscreens contain substances which scatter and reflect light. They are more suited to infants, as there is less chance of causing a contact or hypersensitivity reaction. These sunscreens tend to be colorless after application to the skin and therefore are more cosmetically acceptable than barrier screens.