Here comes summer—and along with it, poolside parties and beach vacations. If you plan on taking refuge from the sun's UV rays under a nice big umbrella, don't think that means you can skip the sunscreen

In fact, it's a good idea to always use more than one sun safety strategy at a time. A study published in the journal JAMA Dermatology compared the effectiveness of sitting in the shade of a beach umbrella with slathering yourself with a high-SPF sunscreen and found that both—if used alone—have their limitations.

The study (funded in part by Johnson & Johnson, the parent company of Neutrogena, which makes sunscreen) involved 81 participants divided into two groups:

• The participants in the first group were assigned to sit under an umbrella that had a UPF of 1,000 (UPF being the fabric equivalent of SPF).

• Those in the second group were given tubes of Neutrogena Ultra Sheer SPF 100+ with instructions to apply the sunscreen liberally to all exposed skin 15 minutes before heading to the beach and reapply it every 2 hours.

Both groups were on the sunny beach between 10 a.m. and 2 p.m., stayed there for 3.5 hours, and didn't go in the water.

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A dermatologist who didn't know which participants were in each group assessed every participant’s skin 22 to 24 hours later. The beachgoers protected only by the umbrellas were more likely to get burned: 78 percent developed sunburn compared with 25 percent of the sunscreen users. The face and the upper chest were the areas most often affected in both groups.

Even though the umbrellas were monitored and repositioned to block the sun from the top down, the shade sitters still got hit with plenty of UV rays. “For one thing, there’s the light that’s reflected up off the sand, which is even more reflective than water,” says Darrell Rigel, M.D., a clinical professor of dermatology at the NYU School of Medicine and one of the study authors.

“Then there’s also redirected light that diffuses and comes in under the umbrella,” Rigel says. “That’s why it’s not pitch black under there.” (Wearing a wide-brimmed hat has the same limitations. It’s great for top-down UV protection but can’t shield you from that reflected light.)

“It’s not surprising that an umbrella didn’t provide sufficient sun protection,” says Joel L. Cohen, M.D., a Denver-based dermatologist and a member of the faculty at the University of Colorado and the University of California at Irvine. “The sun changes positions, and I’ve certainly woken up from a nap under an umbrella to find my face in direct sunlight.”

He also notes that reflection is a huge concern. “I think people forget about the UV rays that are bouncing up off the sand, water, or snow,” Cohen says.

So while seeking shade is a smart strategy, it shouldn’t be your only sun-safety solution. “The real take-home message from this study is that while sunscreen was better than shade,” Rigel says, “sunscreen plus shade is certainly the best protection.”