Q: Does sunscreen expire? Is an SPF of 45 just as effective as SPF 60? I was told that after SPF 30, they’re all about the same. Is that true?
A:Sunscreens reduce the risk of skin cancer and photoaging, a form of premature skin aging caused by sun exposure.
Sunscreen becomes 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 more than a year.
The U.S. 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’re swimming or sweating and the sunscreen washes off. In such cases, the effective SPF is reduced. Be sure to apply sunscreen liberally and reapply 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.
Although sunscreens are highly recommended, there is some evidence that they don’t block all of the cancer-causing rays and that, by giving people the mistaken impression that they are fully protected, may encourage them to spend too much time in the sun.
Here are some additional ways to reduce your UV exposure:
• Avoid the sun during its peak by staying indoors between 10 a.m. and 3 p.m.
• If you have to be outdoors during that time, find shade or use an umbrella.
• Wear long-sleeved shirts and long pants when outdoors, especially during the peak hours of the day. Dark-colored clothing is more protective than light-colored clothing, which allows more UV radiation to pass through.
• Wear a hat when working in the garden or walking outside. A broad-brimmed hat is best.
Dr. Rebecca Campen is an assistant professor of dermatology at Harvard Medical School.
