Ask the Expert

On Cancer: What Should a Person Look for on a Sunscreen Label?

Pictured: Steven Wang Steven Wang, head of the dermatology section at Memorial Sloan Kettering Basking Ridge

Sunscreen is an over-the-counter medicine sold in forms including lotions, ointments, gels, powders, and sprays. It protects skin from ultraviolet (UV) radiation emitted by sunlight.

An estimated 90 percent of the nation’s 3.5 million cases of skin cancer diagnosed each year are caused by exposure to the sun’s UV radiation, according to Steven Q. Wang head of the dermatology section at Memorial Sloan Kettering Basking Ridge, in New Jersey. When used in conjunction with other sun-protection measures such as hats, clothing, and umbrellas, sunscreen can decrease the risk of skin cancer and prevent wrinkles, freckles, and other signs of aging caused by the sun.

Sun Protection Factor

The abbreviation SPF on sunscreen packaging refers to the sun protection factor. It is the standard way to measure the degree of protection that a sunscreen provides. SPF measures protection predominantly against the wavelength of sunlight known as UVB, which is the major wavelength that causes sunburn. Therefore, a product with a higher SPF value offers higher UVB protection.

Broad Spectrum

The SPF value does not measure the degree of protection against UVA — the other portion of the UV spectrum. Both UVA and UVB rays can cause skin cancer. Under US Food and Drug Administration guidelines released last year, products labeled broad spectrum must also provide significant protection against UVA rays.

Ingredients that indicate a product has adequate UVA protection include avobenzone, octocrylene, and zinc oxide.

“When choosing a sunscreen product, you should look for the designation of broad spectrum. I recommend an SPF of 30 or higher for daily use,” Dr. Wang says. “If you will be participating in sports or other outdoor activities, you should look for an SPF of 50 or higher along with a designation of water resistance.”

When and How Much to Apply

To attain the level of protection stated on the packaging, an adequate amount of sunscreen must be used. For an average adult, the ideal amount is 2 milligrams of sunscreen per square centimeter of skin. This translates to about three tablespoons (1.4 ounces) to cover the back, torso, face, legs, and arms.

Sunscreen should be applied 30 minutes before going outside and reapplied every two hours if you are staying outdoors.

“It’s also important to choose a product that you enjoy using, both in its texture and its smell,” Dr. Wang adds. “If you don’t like a product, you’ll be less likely to use it. In addition, you should be sure to use the appropriate amount and reapply frequently to get the best protection from your sunscreen products.”

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