Of the two types of UV rays, UVA are most plentiful, causing wrinkles, spots and skin cancer. Five percent are UVB, which cause sunburn and contribute to skin cancer.
SPF refers to the level of protection from UVB rays. An SPF of 50 filters only 98% of UVB rays. No product provides 100% filtration.
Sunscreen and sunblocks come in a variety of formulas such as lotions, creams, gels, wipes and lip balms. When applied to the skin, they provide protection from UV rays.
Sunscreen uses sun-deflecting chemicals such as avobenzone to prevent the skin from absorbing UV rays. Sunblock reflects and scatters UV rays with titanium dioxide and zinc oxide.
The most effective sun protection are products labeled "broad-spectrum," and protect you from UVA and UVB rays.
UV rays can penetrate clothes. In fact, a light-colored T-shirt provides less protection that SPF 15.