How Does Sunscreen Work?

Absorbing UV rays

Most sunscreens contain organic compounds (as in carbon based, not grown without pesticides), such as para amino benzoic acid or oxybenzone. These compounds work to absorb the sun's rays before they have a chance to reach your skin. Note that they will not block 100% of UV rays. They will simply filter and disperse them, reducing their impact considerably.

Blocking UV rays

Some sunscreens have chemicals that block the sun, providing an extra layer of protection. (Often these sunscreens are referred to as "sun block.") In these sunscreens a chemical such as zinc oxide, works to completely reflect the sun's rays. The rays simply bounce off of the sunscreen it before they can reach your skin. Sometimes you see this kind of sunscreen in colors, like blue or white, since an opaque surface makes this action easier.

Using broad spectrum protection

There are two kinds of UV rays that you need to worry about: UVA and UVB. (The third type, UVC, cannot be absorbed into the skin). UVB rays are the ones most commonly associated with sun damage. However, there is increasing evidence that UVA rays, which are on a different wavelength from UVB, are also somewhat harmful. Sunscreen with broad spectrum protection provides a good shield from both types of UV rays since it contains multiple active ingredients. If a sunscreen has this feature, it should say prominently on the bottle.

Using sun protection factor

All sunscreens have a specific SPF, or sun protection factor. It's used to let the consumer know the strength of the UVB protection in the formula. (UVA is not a factor.) Since some people burn more easily, usually those with fairer skin and hair, there is no universal standard for which SPF to use. Generally it's best to get as high of a number as possible but to always use at least 15. However, no number prevents you from having to reapply sunscreen every couple hours to maintain the highest level of sun safety.