(Bigstock)

Amazon.com reviews have become the indispensable buying guide for all sorts of products for busy Americans who either don’t have time to trek to a retail store or just can’t be bothered. We scrutinize them to figure out which movies to watch, which toasters do the bagel setting right and which toddler booties hold up best.

Given that the marketplace has led you in the right direction with so many other consumer products, you might be wondering whether it’s a good place to read up on the sunscreen you’ve been meaning to buy as summer kicks into high gear. The answer, according to a study published Wednesday by Shuai Xu of Northwestern University's Feinberg School of Medicine, is yes and no.

Xu, a resident in dermatology, found that the selection of sunscreens on Amazon was vast — 6,500 — and that tons of reviews touched on all sorts of criteria, including cosmetic issues (how well the substances absorb, feel, smell or exfoliate), performance (effectiveness, tanning potential) and skin compatibility (whether it might be good for sensitive skin, rosacea, etc.). The 6,500 included sunscreens that also contained moisturizer or were tinted as makeup.

In narrowing down those products to a manageable list, Xu ranked the products by taking into account how many stars they got in their ratings by consumers and how many reviews were offered, and he picked out the top 1 percent for additional scrutiny. The results were published in the journal JAMA Dermatology.

The difference between the high numbered SPF sunscreens is explained. (ACS via Youtube)

For those top 65 sunscreens, Xu and colleagues looked at how well they met American Academy of Dermatology minimum recommendations — that they are at least SPF 30, broad spectrum and resistant to water and sweat — and were surprised to find that 40 percent of these popular sunscreens were deemed insufficient.

He said many of the consumers writing reviews tended to focus on more superficial issues such as smell or feel or on the sunscreen’s value as a cosmetic rather than on its actual sun protection. That may be because sunscreens are no longer stand-alone products, but come in every form of moisturizer and makeup on the market. The ubiquity of sunscreens has made it easier than ever before for consumers to use the products, but it's also created a lot of confusion. A woman might assume she's protected because her morning moisturizer label says it has sunscreen, but she may not realize it's only SPF 10.

Xu said in an interview that the idea for the study came from talking to patients who all asked the same question: Can you recommend a sunscreen?

“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,” he said. “We think of sunscreen as a form of topical medicine. It’s not a luxury product.”

Xu said one important thing to keep in mind is that if a product doesn’t meet AAD criteria for water resistance, that doesn’t mean you can't use it in certain, limited settings. “If it’s the middle of winter in Chicago and you’re not going to be exposed to water, it may be reasonable to forgo that criteria,” he said. However, you clearly don’t want to depend on that at the beach.

The study also found that the price of sunscreen varied greatly — from 68 cents an ounce to $23.47 — but that price wasn’t related to SPF number. Sunscreens that were water-resistant tended to be more pricey, and creams were more expensive than lotions, and lotions more than sprays.

Here’s a closer look at what Xu found:


(JAMA Dermatology)

Two industry groups, the Personal Care Products Council and the Consumer Healthcare Products Association, emphasized that sunscreens are regulated by the Food and Drug Administration in the United States as over-the-counter drugs, and as such, they must undergo rigorous testing before they can be sold to consumers.

They also pointed out that "consumer choice is critical in the variety of sunscreens, as this helps assure that these products will be used." For example, water resistance is an important benefit for sport or beach products but may not be for those looking for a sunscreen "primarily for daily, low-activity use."

"Consumers should look for label statements that meet their needs, water/sweat resistance, moisturizing, etc.," the groups said in a joint statement. "Compliance is a large concern and having a wide product offering, for multiple usage needs, is important to allow consumers to find a sunscreen appropriate for their needs."

(Amazon chief executive Jeffrey P. Bezos is the owner of The Washington Post.)

This post has been updated.

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