What are the active ingredients in sunscreen?

You know you should wear sunscreen to protect yourself from the sun's harmful ultraviolet rays. But what are the active ingredients in sunscreen that make it work?

There are two major types of sunscreen: chemical and physical. Although the terms "sunscreen" and "sunblock" are often used interchangeably, chemical sunscreens absorb UV rays while physical sunscreens, or sunblocks, reflect them.

Chemical sunscreens contain UVB or UVA absorbing ingredients and create a thin film on the skin that reduces ultraviolet radiation (UVR) penetration to the skin. These ingredients include chemicals like avobenzone and benzophenone, which absorb UVR [source: Environmental Protection Agency]. Chemical sunscreens often contain UVB-absorbing chemicals only; however, there are some chemical sunscreens that contain both UVB and UVA absorbers [source: American Melanoma Foundation].

Because they contain ingredients that physically block UVR, sunblocks provide broader protection against both UVA and UVB light [source: American Melanoma Foundation]. Physical sunblocks reflect UV radiation back into the atmosphere using ingredients such as titanium dioxide and zinc oxide [source: UCSF School of Medicine]. These ingredients scatter both UVA and UVB rays, which provides your skin with full protection from sun damage. There are also sunscreen products that contain a combination of chemical and physical sunscreens, which ensure that your skin is completely protected.

If you can't find a sunscreen that contains both UVA and UVB protection, or if chemical sunscreens irritate your skin, look for a sunscreen label that boasts broad-spectrum protection, which protects against all UVR. This is important because a sunscreen's sun protection factor, or SPF, only measures how effective a sunscreen is against UVB rays. There is currently no uniform measure of UVA absorption. [source: Library of Congress].

You now know some of the most important active ingredients to look for when selecting a sunscreen. And once you find one, be sure to apply -- and reapply! To learn more about sunscreens, visit the links on the following page.