Can you trust the SPF number in your sunscreen?

Posted at 8:19 AM, May 17, 2016

Sunscreen protects your skin from developing wrinkles, brown spots and cancer. But can your trust the SPF number on the bottle?

"People look at the SPF, or sun protection factor, and that's very important," says Trisha Calvo, Health Editor for Consumer Reports. "But it's only one part of protecting your skin from the sun."

A Consumer Reports survey found even people who regularly use sunscreens do not always understand what they are buying.

SPF stands for Sun Protection Factor. It is a measure of how well a sunscreen shields skin from the sun's ultraviolet rays. A sunscreen rating of "SPF 15" means 1/15th of the burning radiation will reach your skin.

There are two types of ultraviolet rays, UVA and UVB. The chief cause of sunburns are from UVB rays which only penetrate the top layer of skin. Sunscreens are designed to protect against UVB rays.

UVA rays penetrate deeper into the skin. They can contribute to wrinkles and damage your DNA deep within cells. Conventional sunscreens do not protect you from UVA rays, but broad-spectrum ones are.

Both UVA and UVB rays can increase the risk of developing skin cancer.

"Consumer Reports recommends using a broad-spectrum sunscreen so you're protected against both kinds of rays," says Calvo.

Consumer Reports tested over 60 sunscreens to see whether they deliver the SPF protection they claim.

In the UVB tests, technicians applied sunscreen to volunteers' backs and had them soak in a tub for 40 or 80 minutes, with the length of time depending on a specific product's water-resistance claim.

The area protected by the sunscreen was then exposed to UVB light.

Technicians waited twenty-four hours to check the test area to see if sunscreen worked or if redness developed on the skin, a sign the sunscreen failed. More than 40 percent of the sunscreens tested did not offer the SPF they promised.

Technicians repeated the test to check for UVA protection. Consumer Reports found some broad-spectrum sunscreens had problems. Mineral-only sunscreens also failed to meet their claimed SPF number more often than sunscreens which use either a chemical formulation or a combination of both chemicals and minerals.

There is good news for people who want to enjoy the sun and avoid both UVA and UVB rays. Consumer Reports found some sunscreens aced their tests and are a good value.

The best are Pure Sun Defense SPF 50 ($6), Equate Ultra Protection SPF 50 ($8) and No-Ad Sport SPF 50 ($10).

Consumer Reports also tested spray-on sunscreens. The best are Trader Joe's Spray SPF 50 ($6), Walmart's Equate Sport Continuous Spray SPF 30 ($5) and Dollar General's DG Body Sport SPF 30 ($5).

If you are worried your favorite sunscreen does not offer you the protection you need, Consumer Reports recommends you should choose a product with a SPF 40 or higher. They say that gives you  a better chance of getting at least an SPF 30, the level most dermatologists recommend you use.

To read Consumer Reports' full sunscreen test results, read