How does sunscreen work?

    By combining organic and inorganic active     ingredients.

Sunscreen works by combining organic and inorganic active ingredients. Inorganic ingredients like zinc oxide or titanium oxide reflect or scatter ultraviolet (UV) radiation. Organic ingredients like octyl methoxycinnamate (OMC) or oxybenzone absorb UV radiation, dissipating it as heat. Some sunscreens protect us from the two types of damaging UV radiation: UV-A and UV-B. Both UV-A and UV-B cause sunburns and damaging effects such as skin cancer.

Ultraviolet radiation is broken into three types of wavelengths:

• UV-A: This is the longest wavelength and is not absorbed by the ozone. It penetrates the skin deeper than UV-B.
• UV-B: Responsible for sunburns. It is partially blocked by the ozone layer.
• UV-C: This is totally absorbed by the earth's atmosphere; we encounter it only from artificial radiation sources.

When purchasing sunscreen, the Sun Protection Factor or SPF measures how effectively the sunscreen formula limits skin exposure to UV-B rays that burn the skin. The higher the SPF the more protection the sunscreen will provide against UV-B rays. SPF does not measure UV-A. If you are looking for UV-A protection, the experts recommend that you purchase a product that has broad-spectrum protection.

Related Web Sites

Sunscreen: How to Select, Apply, and Use it Correctly - The Center of Disease Control and Prevention provides a brief list of sunscreen recommendations. American Academy of Dermatology - The Facts About Sunscreens Web site gives information about choosing sunscreen, applying sunscreen, treating sunburns and other questions relating to protecting your skin from the sun. FDA Aims to Upgrade Sunscreen Labeling - FDA wants the labeling on your sunscreen to tell you more about protection against the sun's harmful rays. The Sun, UV, and You - A guide to the UV index and Sun-Safe Behavior. This Web site from the EPA provides information about UV, health risks of sun exposure, and how to protect yourself from the damaging effects of the sun. Also has a section about ozone depletion. Climate Prediction Center: Current UV Index Forecast - This Web site provides the UV index at high noon for the United States. UV Radiation: NASA - NASA Advanced Supercomputing Division educational resource on ultraviolet radiation contains an introduction to ultraviolet radiation and the health effects of UV-B radiation. References are also cited at the end of the article.

Further Reading

Reisch, Marc. Sunscreens: active ingredients prevent skin damage. Chemical & engineering news, v. 80, June 24, 2002: 38. Accessible online at URL: http://pubs.acs.org/cen/whatstuff/stuff/8025sunscreens.html Sunscreens: development, evaluation, and regulatory aspects. Edited by Nicholas J. Lowe, Nadim A. Shaath, and Madhu A Pathak. 2nd ed. New York, Marcel Dekker, c1997. 792 p. UV-B radiation and ozone depletion: effects on humans, animals, plants, microorganisms, and materials. Edited by Manfred Tevini. Boca Raton, FL, Lewis Publishers, c1993. 248 p. United States. Adequacy of protection from sunglasses and sunscreens: hearing before the Ad Hoc Subcommittee on Consumer and Environmental Issues of the Committee on Governmental Affairs, United States Senate, One Hundred Second Congress, Second session, June 5, 1992. Washington, U.S. G.P.O., 1993. 294 p.

For more print resources...
Search on "sunscreen," "uv" and "ultraviolet" in the Library of Congress Online Catalog.

Society leaders display 200 years of beach attire at Cape May Sun Tan Cabana Club. Underwood and Underwood, 1931. Prints and Photographs Division, Library of Congress.

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