What Sunscreen Numbers Mean? Top-Rated SPF Products For This Summer

The best sunscreens that can be used to protect the skin this summer have been named by Consumer Reports. The report rated 73 lotions, sprays, and sticks in terms of effectiveness and accuracy of SPF labeling.

SPF, or sun protection factor, refers to its ability to shield from the sun’s ultraviolet rays. The SPF number is the level of protection a sunscreen provides against the rays, which is the main cause of sunburn and a contributor to skin cancer. In general, it takes about 10 to 20 minutes for a person’s skin to start burning if he or she is not using a sunscreen.

The report included sunscreens labeled SPF 30 or higher, with a recommendation of buying a chemical sunscreen with an SPF of 40 or higher.

"We do our own scientific, laboratory-based testing to identify differences in performance and give consumers a comparative evaluation," Trisha Calvo, deputy editor of health and food at Consumer Reports, told CBS News. "Every sunscreen is tested at the lab in the same way — and we use sunscreens we buy off the shelves, the way a consumer would."

The top 5 sunscreens, according to Consumer Reports are La Roche-Posay Anthelios 60 Melt-In Sunscreen Milk, Equate (Walmart) Sport Lotion SPF 50, BullFrog Land Sport Quik Gel SPF 50, Coppertone WaterBabies SPF 50 Lotion, and Coppertone Ultra Guard SPF 70 Lotion.

The report warned consumers about claims on sunscreen bottles, including "sport," "dermatologist recommended," and "natural" or "mineral," that are not regulated by the FDA. No mineral sunscreens made Consumer Reports' list of recommendations this year.

An SPF 15 product would prevent skin from burning for 15 times longer — so about 150 to 300 minutes, or about 2.5 to five hours. However, that doesn’t mean that a person is fully protected for those five hours. Dermatologists highly recommend reapplying sunscreen every two to four hours, as it can rub off or get washed off while swimming or sweating.

For many, the numbers can get confusing. "SPF is not a consumer-friendly number," Florida dermatologist James Spencer told WebMD. "It is logical for someone to think that an SPF of 30 is twice as good as an SPF of 15 and so on. But that is not how it works."

Below are five facts that many people using sunscreens are less aware of, according to Environmental Working Group.

1. There’s no proof that sunscreens prevent most skin cancer.

2. The common sunscreen additive vitamin A may speed development of skin cancer.

3. European sunscreens provide better UVA protection.

4. Sunscreen doesn’t protect skin from all types of sun damage.

5. Some sunscreen ingredients can cause skin allergies.

According to the Centers for Disease Control and Prevention, skin cancer is the most common cancer in the United States. Reports say that 5.4 million Americans are diagnosed with skin cancer each year, and that one in five people will develop skin cancer in the course of a lifetime.