Don’t fall for SPF inflation: No sunscreen offers complete protection from the sun.

SPF, or Sunscreen Protection Factor, measures a sunscreen’s protection from UVB (Ultraviolet B) rays, which causes sunburn and contributes to skin cancer. SPF does not measure a sunscreen’s protection from UVA (Ultraviolet A) rays, which penetrate into the skin’s thickest layer and can suppress the immune system. (A compromised immune system heightens the risk of skin cancer.)

“But don’t let the fear of sunburn or skin cancer chase you indoors,” says Dr. W. Richard McQueen Jr., an internal medicine specialist at Hartford HealthCare Medical Group. “Just take the right precautions.”

Do you know what a sunscreen’s SPF value means? It represents the number of minutes it takes to get the equivalent of one minute of ultraviolet rays. So after applying an SPF 20, your body will be exposed to the equivalent of one minute of ultraviolet rays for every 20 minutes spent in the sun.

“A shot glass is one ounce. Apply that amount every two hours while you’re outside on exposed areas,” says Dr. Frank Santoro of Hartford HealthCare’s Skin Cancer Prevention Clinic. “Apply a thin layer on all areas 15 minutes before going outside.”

Higher SPF values offer more protection, but at a diminishing rate. An SPF 15 sunscreen filters about 93 percent of UVB rays, an SPF 30 about 97 percent, an SPF 50 about 98 percent and SPF 100 about 99 percent, according to the American Cancer Society.

“SPF 30 is the magic number,” says Santoro.

When shopping for a sunscreen, look for a product that protects against all types of damage caused by the sun.

“Make sure the bottle says ‘broad spectrum,’” says Dr. Robert Piorkowski, a surgical oncologist at Hartford Hospital, “so you are protected from UVA and UVB rays.”

  • Food and Drug Administration regulations require a “Skin Cancer/Skin Aging Alert” warning on any sunscreen that’s not broad spectrum or has an SPF value between 2 and 14.
  • Sunscreens that make water-resistance promises must indicate how long the claimed SPF level will last, either 40 or 80 minutes, while swimming or sweating.
  • Manufactures cannot claim a sunscreen is either waterproof or sweatproof, nor can it claim instant protection when first applied or protection for more than two hours without reapplication.
  • The FDA rates SPF 15 as the minimum for protection against sunburn and skin cancer, but the American Cancer Society recommends SPF 30 or higher.