How do sunscreens work?
The active ingredients within sunscreens absorb, reflect, or scatter ultraviolet (UV) radiation, and thereby alter how the body responds to this radiation. Sunscreens typically contain a combination of different chemicals that are known to be effective for certain wavelengths of UV light. Some chemicals work better than others, however, as do some combinations of chemicals. For years, manufacturers created sunscreens that were only effective at screening out UVB radiation, since this is the type of radiation that was known to cause sunburn and lead to skin cancer. More recently, manufacturers have worked to create sunscreens that will protect the skin from both UVA and UVB radiation, since scientists realized that UVA radiation is also harmful. All sunscreens provide UVB protection, but only some protect against UVA rays (FDA 1999).
