There hasn’t been much evidence that anything above SPF 50 is any more effective, until now.

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In today’s “Well, duh!” news, a new study in the Journal of the American Academy of Dermatology indicates that sunscreen products with a higher sun protection factor (SPF) might actually protect you better than those with a lower SPF. While this seems like it should be totally obvious, it isn’t, because sunscreen is one of the most confusing products out there in terms of testing, marketing, and usage.

Consumers don’t understand SPF very well; they don’t apply enough sunscreen to provide the protection that is achieved in lab settings, formulas are unappealing, people are afraid of ingredients, and there have been conflicting recommendations about whether a higher SPF is better. To further confuse things, the Food and Drug Administration has noted that there isn’t enough data to prove that anything over SPF 50 adds more protection. This study addresses a couple of those issues.

First, though, what does SPF mean?

The SPF (sun protection factor) number indicates the amount of theoretical protection you get compared to wearing nothing. So if it takes 20 minutes to burn without protection, it will take 15 times longer — five hours — while wearing SPF 15. Or, to think of it another way, it provides 15 times the protection of wearing nothing.

There are many caveats in that figure, though, including the fact that efficacy decreases after about two hours, requiring reapplication, especially if you get wet. Also, SPF only measures protection against UVB exposure, not UVA. Both forms of ultraviolet radiation have been shown to cause cancer. (Look for “broad spectrum” products, which contain ingredients that cover both.)

What’s even more confusing is that protection is not linear, meaning that SPF 30 doesn’t cover you twice as well as SPF 15. SPF 15 protects you from about 93 percent of UVB rays at any given moment, SPF 50 from 98 percent, and SPF 100 from 99 percent. Seems like a minimal difference, but then you have to look at the rays that still do get through. (This one-minute video is incredibly helpful for visualizing it.) Of the 2 percent of rays that get through, SPF 100 will cover 1 percent more than SPF 50.

Finally, and most crucially, that SPF number is derived in a lab with an amount of product that no human ever actually uses, according to Dr. Darrell Rigel, a dermatologist at the Schweiger Dermatology Group and a clinical professor at NYU, who is one of the new study’s authors. “If you were to put that on, [you would] be white as a sheet of paper. It would be ridiculous. People use approximately 25 to 50 percent of the rated amount in the real world, and therefore, they’re getting 25 to 50 percent of the SPF,” Rigel explained on a call.

The sunscreen study

The purpose of the study was to determine whether a higher SPF product made a difference in the real world, with the way people really use sunscreen. The authors of the study looked at 199 subjects who went skiing on a sunny March day in Vail, Colorado. The group was split pretty evenly by gender, and they had Fitzpatrick type one through three skin, meaning they were fairly pale and prone to burning.

They were given two bottles of sunscreen, marked right or left, and were asked to apply one to each side of their faces. One contained SPF 100 and one SPF 50. The bottles were weighed before and after to determine how much was used. The subjects also kept a diary every half-hour to track whether they were inside or out and whether they reapplied. The next day, the amount of facial redness was evaluated. It was a randomized and double-blinded study, so neither the subjects nor the dermatologist doing the evaluation afterward knew which product went on which side of the face.

On average, the subjects were out in the sun for about six hours total. The SPF 100 performed a lot better than the SPF 50 after the authors looked at various data points. More than 55 percent of the subjects were burned more on the SPF 50 side than on the SPF 100 side. Sunburn severity was also worse on the SPF 50 side.

“Overall, you were 11 times more likely to burn on the SPF 50 side than the SPF 100 side. It didn’t matter what your skin type was, it didn’t matter how many times you reapplied, the SPF 50 side always did worse than the 100,” said Rigel. “What mattered was the SPF 50 did not perform as well as the SPF 100 in a real-world setting. That was the conclusion.”

One potential limitation is that the study only measured the effects over one day. Additionally, the study was funded by Johnson & Johnson, which owns Neutrogena. A Neutrogena SPF 100 product and a Banana Boat SPF 50 product (which is owned by Edgewell Personal Care) were used. Both are broad spectrum but have slightly different ingredient profiles.

Why this all matters to you, the sunscreen user

Unlike cosmetics, the FDA does regulate sunscreens because the ingredients are considered to be over-the-counter drugs. The FDA has considered a mandate that companies can only label sunscreens up to SPF 50+, which many other countries do, stating that there was no good evidence proving that higher SPFs are better.

Back in 2010, a group published a study looking at sunscreens with an SPF 85 and it yielded similar results as this one. The FDA had some issues with the methodology, though, and the authors of this study designed it to meet those recommendations, according to Rigel, who was also an author of the 2010 study.

Over the past five years or so, the messaging has been pretty clear that using anything over 50 is probably unnecessary. You may now hear those recommendations changing. “The FDA is actually using the paper now to take a look at this and they probably will not be putting an SPF cap of 50+ on sunscreens at this point,” said Rigel. But don’t expect to see anything much over SPF 100 hitting the market. Rigel said it’s very difficult to chemically engineer a product much higher than that.

While this is only one single study and you can’t generalize a ton from it, we will likely see more SPF 100 products for sale now. And yep, those cost more. At Target, Neutrogena’s Sheer Dry Touch SPF 100 sunscreen is $8.10 for three ounces; the SPF 55 version is $7.11 for the same size.

The bottom line still, though, is that the best sunscreen practice is to be consistent about using it.