During the recent decades, the thickness of the ozone layer over the northern hemisphere has declined by 10 to 40 percent during the winter and spring months. Since ozone is the major barrier protecting the earth from dangerous short wave UV-radiation (UVB), the depletion in the ozone layer consequently increases the amount of UV-radiation reaching the earth's surface. As a rule a 10 percent reduction in the ozone layer causes ca. 20% increase in UV-radiation and a 40% increase in skin cancers. Thus relatively minor changes in ozone layer thickness may a have marked impact on the health of humans. Skin cancer is the most common cancer in humans, i.e. in Finland about 4000 new basal cell carcinomas, 700 other skin cancers, mostly spinous cell carcinomas and 500 melanomas occur yearly. Up to recent years the incidence of skin cancers has steadily increased in northern countries. As an explanation, changes in sunbathing habits have been suggested to play a central role. Due to the high mortality rate in melanoma, and marked morbidity in other skin cancers, it is important to try to prevent skin cancers and inform the public about the risks of excessive sun exposure, and of the ways in which the skin can be protected. Proper clothing and use of sunscreens have been shown to reduce the incidence of both melanomas and other skin cancers. Furthermore, it is important to identify those at high risk for acquiring skin cancers, like individuals with type 1 skin character (fair skin which burns easily), or numerous dysplastic nevi, or a family history of skin cancers.