UV, or ultraviolet, rays are the sun's "invisible" burning rays. They can cause sunburns, and in some cases skin cancer.
There are three types of UV rays:
UVA: Are more constant year-round and penetrate deeper into the skin's layers; UVA rays are also harmful and contribute to burning, premature aging of the skin, and the development of certain forms of skin cancer.
UVB: Are the primary cause of sun burning, premature aging of the skin and the development of skin cancer.
UVC: Are blocked by the ozone layer and do not reach the earth's surface.
