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Sunscreen: Answers to your burning questions

Know how to select and apply a good sunscreen to protect your skin from sunburn and other skin damage.

By Mayo Clinic staff

If you're like most people, you enjoy spending time outdoors and feeling the heat of the sun on your skin. But not all the sun's rays are pleasing. Ultraviolet (UV) light — invisible, but intense rays from the sun — can damage your skin and increase your risk of skin cancer.

Though it's not the only safeguard you need to take, sunscreen is one of the easiest ways to protect your skin and is a good first line of defense.

Here's how you can get the most protection from your sunscreen.

How do sunscreens work?

Sunscreen absorbs, reflects or scatters UV light. It's divided into three wavelength bands — ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC). Only UVA and UVB rays reach the earth.

Sunscreens provide either physical or chemical protection from UV light.

  • Physical sunscreens form an opaque film that reflects or scatters UV light before it can penetrate the skin. These sunscreens contain ingredients, such as zinc oxide and titanium dioxide, which protect against both UVA and UVB rays. Original formulations of physical sunscreens remained white when applied to the skin. Newer formulations blend more with your skin tone and are less noticeable.
  • Chemical sunscreens absorb UV rays before they can cause any damage. They contain one or more ingredients, such as avobenzone or oxybenzone, which absorb UVA or UVB rays. For broad protection, chemical sunscreens often contain more than one ingredient to protect against both UVA and UVB rays. A newer over-the-counter sunscreen contains mexoryl (Anthelios SX) and offers protection against both UVA and UVB radiation.

Who should use sunscreen?

If you spend time outdoors during daylight hours, you need to use sunscreen even if you have darker skin pigment, tan easily and can tolerate longer periods of sun exposure without burning. Regardless of skin type, the sun's energy penetrates deeply into the skin and damages DNA of skin cells. This damage may ultimately lead to skin cancer.

Children are especially susceptible to the harmful effects of the sun, so take extra steps to protect their skin and to prevent sunburns. Babies younger than 6 months should be kept out of direct sunlight because their skin is even more fragile. Use sunscreen on an infant only if you're unable to keep him or her out of the sun and are unable to cover exposed skin. Use a small amount on uncovered areas, such as on hands or ears, and check for any skin reactions.

What is an SPF?

All sunscreens products include an SPF, which stands for sun protection factor. The SPF number is a measurement of the amount of UVB protection — the higher the number, the greater the protection. Currently, there's no standard rating system that measures UVA protection.

SPF is not an indication of how much time you can spend in the sun. For example, if you use a sunscreen with an SPF 30 rather than one with an SPF 15, it doesn't mean you can stay in the sun twice as long. In reality, an SPF of 15 filters out about 93 percent of the UVB rays; SPF 30 filters about 97 percent of UVB rays. The beneficial effects of sunscreen decreases over time, so after a few hours the difference between the two may be even less.

Don't rely on the SPF factor to decide how long you're safe in the sun. And don't count on your skin to tell you when you've had too much sun. It may take up to 24 hours for a sunburn to develop fully.

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References
  1. Sunscreens/sunblocks. American Academy of Dermatology. http://www.aad.org/public/publications/pamphlets/sun_sunscreens.html. Accessed Jan. 20, 2009.
  2. The burning facts. Environmental Protection Agency. http://www.epa.gov/sunwise/doc/sunscreen.pdf. Accessed Jan. 20, 2009.
  3. Sunscreen drug products for over-the-counter human use: Final monograph. Food and Drug Administration. http://www.fda.gov/cder/fdama/fedreg/sunscreen.pdf. Accessed Jan. 20, 2009.
  4. Skin cancer: Questions and answers. Centers for Disease Control and Prevention. http://www.cdc.gov/cancer/skin/chooseyourcover/qanda.htm. Accessed Jan. 20, 2009.
  5. FDA approves a new over-the-counter sunscreen product. U.S. Food and Drug Administration. http://www.fda.gov/bbs/topics/NEWS/2006/NEW01417.html. Accessed Jan. 20, 2009.
  6. Parenting corner Q&A: Sun safety. American Academy of Pediatrics. http://www.aap.org/publiced/BR_SunSafety.htm. Accessed Jan. 21, 2009.
  7. Facts about sunscreen. American Academy of Dermatology. http://www.aad.org/media/background/factsheets/fact_sunscreen.htm. Accessed Jan. 21, 2009.

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March 27, 2009

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