Although sunlight is essential for human life, daily exposure to the sun over a lifetime is a major cause of skin damage, including wrinkling and skin cancer. The process is characterized by clinical, histological and biochemical changes that differ from changes in chronologically aged skin. While chronologically aging skin changes “gracefully”, photo damaged skin will age much faster and “ungracefully” displaying tough, leathery, dry, rough skin, among a few of the visible signs. Many of the skin changes attributed to aging are, in fact, signs of sun-induced skin damage. Sunscreens work by scattering, absorbing or reflecting UV rays. Sun blocks are opaque substances, zinc oxide and titanium dioxide, work on top of the surface to deflect UV rays away from the skin. Chemical Sunscreens work by changing UV rays into heat, and release heat from the skin. Sunlight exposes people to two kinds of UV light: UVA and UVB. Virtually all sunscreens provide some level of protection against UVA and UVB rays.
The solar spectrum is divided into the following key regions:
Visible Light (400-760nm)
SPF sunscreen numbers only indicate the amount of time one can stay in the sun without burning. The application of an SPF 15 sunscreen should provide protection about 15 times longer than no sunscreen at all. SPF protection does not increase proportionally with SPF number. SPF 30, for example, absorbs 97% of sun burning rays, while an SPF of 15 indicates 93% absorption. SPF numbers lower than 15 probably won't offer enough protection, while those higher than 30 may not offer any additional benefits.