Ultraviolet (UV) radiation from the sun can cause damage to living tissue if it penetrates the earth's atmosphere.

• UV-A is the least damaging; 50% reaches the earth's surface.

• UV-B is higher energy, but most is blocked by ozone (O₃) and only 10% reaches the earth's surface.

• UV-C is the most damaging, but virtually all is absorbed by oxygen gas O₂.