Researchers at Consumer Reports independently evaluated the Sun Protection Factor value of 65 sunscreen products -- including lotions, sprays and sticks -- and found that 43% of them had less SPF than the label promised.
Any reduction would block fewer UVB rays from sunlight, which can cause sunburn and skin cancer.
The American Academy of Dermatology recommends choosing a sunscreen that is at least SPF 30, which would block 97% of UVB rays.
"[Sunscreens] should live up to the claim on their label, and in our test we found some of them did not," said Patricia Calvo, Consumer Reports' deputy content editor for health and food, who worked with the researchers to create Tuesday's report.
The findings are consistent with previous Consumer Reports studies, she said. Over the past four years, since the U.S. Food and Drug Administration updated requirements for how sunscreen manufacturers label and test their products, 48% of sunscreens have fallen short of their SPF claim.
How many are incorrect?
In this year's report, 13 of the 35 sunscreen lotions that were tested had an SPF less than 30, despite all claiming to be at least SPF 30. This included two of the 18 sprays and three of the eight face sunscreens.
The most problematic products were Banana Boat Kids Tear-Free, Sting-Free Lotion and CVS brand Kids Sun Lotion, which were both labeled as SPF 50 but were found to have only SPF 8.
The majority of products that did not live up to their SPF claims fell short by about 10 or 15 points. Consumer Reports recommends that "you look for a chemical sunscreen that is at least SPF 40 because that will give you the best chance of getting SPF 30," Calvo said.
Sunscreens with chemical active ingredients, such as avobenzone and ecamsule, were found to perform better than those with "natural" or mineral active ingredients such as titanium dioxide and zinc oxide.
Consumer Reports notified Banana Boat and CVS because their SPF values were found to be so much lower than claimed.
Edgewell Personal Care -- which produces Banana Boat -- responded, "The lot of Banana Boat Kids SPF 50 lotion tested by Consumer Reports met the rigorous specifications in our manufacturing and testing process, including the level of active ingredients present required to achieve the formula's SPF value."
CVS said it retested its products and found that they too met the stated SPF rating of 50.
Edgewell Personal Care, which also produces Hawaiian Tropic, repeated its statement to CNN: "[Our products] met our rigorous specifications that adhere to FDA-mandated testing requirements."
Other companies, including Bayer -- the maker of Coppertone sunscreen products -- gave similar responses.
Bayer said its products "meet or exceed all SPF and broad spectrum requirements set forth by the FDA," ensuring that its sunscreens are "rigorously evaluated for safety and efficacy, including for SPF and broad spectrum, by independent investigators, dermatologists, pediatricians and scientists."
Why did some sunscreens fare poorly?
One reason for the discrepancy could be differences between how Consumer Reports and sunscreen manufacturers tested the products.
For the new study, researchers tested the ability of a sunscreen to protect participants from sunburn for 80 minutes after they had been soaked in water, whereas manufacturers tend to assess sunscreen performance on people who have not gotten wet.
Because of this difference, it is possible that part of the problem with the sunscreens in the new study was that they did not live up to their claims of being water-resistant.
"Sunscreens are supposed to maintain their SPF level through water immersion for the amount of time they claim to be water-resistant," Calvo said, explaining that for most products, this is 80 minutes.
"Their protocol sounds very different, but it is possible that the Consumer Reports study is testing in a more realistic fashion. ... [It] seems geared toward the person going on vacation who will sit by pool or ocean," said Dr. Cameron Rokhsar
, associate clinical professor of dermatology at Mount Sinai Hospital in New York. He added that this would be very different from someone using them every day for protection while walking outside for a few minutes.
"My impression all along has been that the sunscreen industry is involved in a game of numbers to sell more products, by having a higher SPF rating on their tubes," he said. Rokhsar suggests the FDA keep a closer eye on the industry, like it does on the pharmaceutical industry, to ensure more rigorous testing.
As far as consumers are concerned, however, it does not really matter as long as sunscreen products have an SPF of at least 30, according to Rokhsar.
Products with SPF greater than 30 provide only marginally better protection. While SPF 30 blocks 97% of UVB rays, SPF 50 and 100 block 98% and 99% of rays, respectively.
The real benefit comes from frequent -- and liberal -- application, ideally every two hours.
The American Academy of Dermatology recommends using an amount of sunscreen that is roughly equivalent to the size of the palm of your hand and applying it all over your body.
Which come out top?
The Consumer Reports study recommended a number of sunscreen products that met its SPF claims and offered excellent or very good UVA protection. UVA rays increase the risk of skin cancer, like UVB, but also cause wrinkles and leathery, sagging skin.
The top five sunscreen lotions, according to the report, are:
- La Roche-Posay Anthelios 60 Melt-In Sunscreen Milk SPF 60
- Pure Sun Defense SPF 50
- Coppertone Water Babies SPF 50
- Equate Ultra Protection SPF 50 (Walmart brand)
- No-Ad Sport SPF 50
But it's not all about sunscreen. The American Academy of Dermatology also advises people to wear protective clothing and stay in the shade to reduce their risk of skin cancer.