When summer arrives, people turn to sunscreen to protect themselves from the sun. But a new study casts major concern over whether the most popular sunscreen brands actually protect users. A team of researchers led by a dermatologist scrutinized highly rated sunscreens on Amazon, and uncovered a shocking statistic: 40 percent of those sunscreens don’t comply with American Academy of Dermatology (AAD) guidelines for sun protection.

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Dermatologist Shuai Xu worked with colleagues at Northwestern University and the Duke University School of Medicine to publish an original investigation into sunscreen in the journal JAMA Dermatology in early July. Xu’s team found 6,500 sunscreens on Amazon. Based on how many customers reviewed a product and how highly they rated the product, Xu’s team selected the top 1 percent – 65 sunscreens – to study. 26 of the products “did not adhere to AAD guidelines.”

Related: EWG’s 2016 best and worst sunscreen lists are out – is your favorite listed?

AAD guidelines say a sunscreen should have a SPF of at least 30 (and it should be noted anything past SPF 50 likely doesn’t offer more protection), be resistant to water, and protect against UVA and UVB rays (labeled as “broad spectrum”).

Some of the sunscreens that failed to meet guidelines are Blue Lizard Australian Sunscreen, Sensitive SPF 30+; Neutrogena Oil Free Moisture SPF 35; and Eucerin Daily Protection Moisturizing Face Lotion, according to Xu’s study. All three of those sunscreens had the required SPF and were labeled broad spectrum but were not water resistant. The researchers found water resistant sunscreens were generally more expensive. They also discovered sunscreen prices aren’t necessarily related to SPF.

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Xu said, “As doctors, we want to have some input and insight into what consumers are using, because sunscreen is a really important part of skin health. We think of sunscreen as a form of topical medicine. It’s not a luxury product.”

Via The Washington Post

Images via Wikimedia Commons and Skeyndor Cosmética Científica on Flickr