It is customarily said that sunshine is good for us. While the sun is essential for the proper balance of our health, paradoxically it can become our worst enemy, especially in case of prolonged exposure or inadequate protection. The sun's rays in such circumstances can produce dramatic consequences. Of all the ultra-violet rays emitted by the sun, the UVC's are the most dangerous for humans. They are, however, normally filtered out 100% by the ozone layer. The UVB's, only 30% of which are filtered out by the ozone layer, are responsible for the majority of skin problems (burns, cancer, etc.). As for the UVA's, they are not filtered out at all by the ozone layer and are mainly responsible for ageing of the skin through the destruction of the basal cells.
All that means you must use the most effective protection with top-quality sun tan products.