Broad spectrum sunscreen protects the skin from both UVA and UVB rays. UVA rays are longer waves that cause skin aging, whereas UVB rays are shorter and cause the skin to burn. Sunscreen should be applied 15 to 20 minutes before sun exposure and should be reapplied every two hours or after swimming or sweating. Chemical sunscreens, the most common form of sun protection, are made up of carbon compounds and absorb ultraviolet rays. Mineral sunscreens contain titanium dioxide or zinc oxide and work by sitting on the skin and reflecting ultraviolet rays.Want to read more? Subscribe to one of our monthly plans to continue reading this article.