Because of the tilt of the earth in relation to the sun, tropical areas receive stronger solar radiation year-round, than other areas in the world. In nontropical areas, solar radiation is stronger in summer than in winter because the earth's tilt puts that part of the world closer to the sun in summer. Solar radiation includes, of course, visible light. UV radiation at high doses increases the risk of basal cell carcinoma and malignant melanoma .
Mild sunburn is a first-degree radiation burn.
In a mild sunburn, the skin is red and painful. The outer layers of the epidermis peel in 3-6 days, with itching and redness persisting up to a week or more. Extreme sunburn can also be a second-degree burn. Third-degree sunburn is rare, and likely requires several days of exposure. The first commercial sunscreen was developed in 1928, and contained benzyl salicylate and benzyl cinnamate .