What are the characteristics of UVA rays?
More UVA rays reach the earth’s surface than do UVB rays and UVA rays outnumber UVB rays by a ratio of 9 to 1. In addition, UVA rays do not undergo seasonal and daily changes as do UVB rays, so human skin is exposed to continuous UVA radiation. UVA also penetrates more deeply into the skin, directly to the dermis.