If you think sitting under an umbrella at the beach means you don't need to apply sunscreen, new research shows you're mistaken.

A study published recently in JAMA Dermatology tested the effectiveness of shade from an umbrella versus sunscreen with a Sun Protection Factor (SPF) of 100. For the study, 81 participants spent more than three hours on the beach in Texas in the middle of the day, either sitting under an umbrella or lathered in sunscreen. Those who used the umbrella stayed under the umbrella the whole time and were constantly monitored and adjusted to reduce sun exposure.

The end result? The umbrella was not nearly as effective at blocking UVB radiation, the kind that leads to sunburns. The researchers found that 78 percent of participants seeking shade under an umbrella later developed a sunburn, compared to 25 percent who got a burn despite the sunscreen.

This research comes a few years after another study published in the same journal concluded that umbrellas were, in fact, sufficient sun protection. The difference, though, is that study measured UV radiation through handheld umbrellas.

Many umbrellas come with a UPF (Ultraviolet Protection Factor) rating, which is determined by how many UV rays an umbrella blocks. UPF is different than SPF, which is used to rate sunscreens. Doctors usually recommend clothing, hats or umbrellas with a UPF of 50 or more. Generally, darker, more tightly woven fabrics have a higher rating.

Those uncontrollable UV rays

Man on beach holding umbrella over him If you're using an umbrella as sun protection, make sure it's UPF 50 or more. (Photo: Alexander Chaikin/Shutterstock

You might think an umbrella with a high UPF would effectively protect against sunburns. But the recent study shows it doesn't, and it offers more practical ramifications.

According to Florida-based dermatologist Dr. Russel Glaun, the issue could be related to reflected UV rays. “If one assumes that the umbrellas used in the study were at least UPF 50 and the subjects did not leave the protected area then, in theory, the protection should have been roughly equivalent to the SPF 100 sunscreen,” explains Glaun. “The major variable, then, would be UV rays, which are not shielded by the umbrella such as that due to reflection off sand, water, etc. as well as lower angled UV rays at different times of the day.”

In fact, Glaun says that the actual amount of UV rays you take in merely by reflection is startling. “Up to 25 percent of UV rays can be reflected by sand or sea foam. And because of indirect UV exposure by reflection, you can be exposed to as much as 80 percent of the sun's radiation when you are under an umbrella.”

Experts say it’s best to use a multi-faceted approach when it comes to sun protection: shade, sunscreen and staying out of the sun during peak times. Bottom line: “Make sure that your sunscreen is at least SPF 30 and appropriately applied,” recommends Glaun. “If you are using your umbrella for protection, make sure it's UPF rated 50 or greater, wear sun-protective clothing and sunscreen on exposed skin.”