So what's the big deal? Are not all sunscreens created equal Not according to modern research. Uv rays come two varieties, UVA and UVB UVB rays are the ones that burn the skin. But UVA rays penetrate the outer layer of skin where they break down skin proteins, damage cells and DNA. decrease the skin's immunity and generate harmful free radicals. This in turn leads to wrinkles. sagging skin, brown spots. yellow discoloration, and various types of skin cancer