Most people know that one should protect themselves from the sun and that UV rays are harmful because it can cause cancer and other problems. Some also know that UV rays together with air pollution make up the two main causes of premature aging of the skin. But what exactly are UV rays? How do they affect the skin? Why are they harmful to us? And what is sun protection factor? We have gathered all the information you need in two articles, one on sun protection factor and SPF and one on UVA and UVB rays.