Ask An Expert: Sunscreen Effectiveness

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Ask An Expert: Sunscreen Effectiveness

Question:

Does sunscreen expire? Is an SPF of 45 just as effective as SPF 60? I was told that after SPF 30, they are all about the same. Is that true?

Answer:

Sunscreens reduce the risk of skin cancer and photoaging, a form of premature skin aging caused by sun exposure. Sunscreen formulations become less stable over time, which means that they do expire. Check to see if the sunscreen tube or bottle has an expiration date, and discard by that date. If there isn't a date listed, discard any sunscreen that you have had over a year to make certain that it is still effective.

The Food and Drug Administration regulates sunscreen products as over-the-counter drugs. It is important to use a sunscreen with at least an SPF of 15. This means that you can stay in the sun without burning 15 times as long as you can without sunscreen. An SPF of 45 means that you can stay in the sun without burning 45 times as long as you can without sunscreen, and an SPF of 60 means that you can stay in the sun 60 times as long without burning than you can without sunscreen. But these numbers do not hold true if you are swimming or sweating and the sunscreen washes off. In such cases, the effective SPF is reduced. Be sure to apply sunscreen liberally and re-apply often.

Sunscreens protect primarily against UVB rays from the sun. The sun's UVA rays, however, can still damage skin and increase the risk of skin cancer. Choose a sunscreen with both UVB and UVA protection. Generally, sunscreens with a higher SPF -- and with certain ingredients such as avobenzone, meradimate, ecamsule and oxybenzone -- give better protection against UVA. Check the label to make sure that your sunscreen offers protection against both types.

Rebecca Campen, M.D., J.D. is an Assistant Professor of Dermatology at Harvard Medical School and former Deputy Director of the Harvard/Massachusetts General Hospital Cutaneous Biology Research Center (CBRC). She currently serves as Senior Advisor to the CBRC and divides her time between clinical practice of dermatology at the Massachusetts General Hospital and private practice in Savannah, Georgia. Dr. Campen is the author of two books for medical students and residents, Going Into Medical Practice and Blueprints in Dermatology.

Last updated:	July 23, 2007