Gut Check looks at health claims made by studies, newsmakers, or conventional wisdom. We ask: Should you believe this?
Sunscreen protects against sunburn better than beach umbrellas, concluded a study last week in JAMA Dermatology.
Tell me more:
Researchers randomly assigned volunteers, all without sunburn, to either of two groups. Forty were asked to apply sunscreen with a 100 sun protection factor, or SPF, 15 minutes before going to a Texas beach on a sunny August day from 10 a.m. to 2 p.m. They were asked to apply it again every couple of hours, and to stay out of the water. Another 41 volunteers were instructed to skip the sunscreen but stay under a standard canvas beach umbrella for that period. Their positions were monitored by the researchers so that as the sun moved, they were never in direct light.
A day later, clinicians who didn’t know who was in which group evaluated everyone for sunburn. In the umbrella group, 32 of the 41 were sunburned in a total of 142 places (face, upper chest, right arm, and the like) compared with 10 of the 40 sunscreeners in 17 total spots. That works out to a threefold reduction in the risk of sunburn for the sunscreen group.
The fact that the lead author of the study is an employee of Johnson & Johnson, which makes the Neutrogena sunscreen used in the study, and that other authors consulted for J&J, is a red flag: Time and again, including last week, research has shown that when scientists have financial ties to a company, they’re more likely to get results that make its products look good than are researchers with no such conflict of interest.
But the findings jibe with other data — most fundamentally, that ultraviolet radiation, especially the shorter-wave ultraviolet B that’s responsible for sunburn, gets scattered by clouds and reflected by surfaces such as concrete and dry sand. Both processes cause UVB to come at you from below and sideways, not just from above. Only shade so deep that you can’t see the sky provides total UVB protection, so beach umbrellas don’t. “There’s shade and there’s shade,” said senior author Dr. Darrell Rigel of New York University, who is a J&J consultant.
Earlier studies have measured the UV under beach umbrellas, finding that they have the equivalent of SPFs from 3 to 10. That means as much as one-third of UV gets through — though other studies find as much as 84 percent does. You can get a noticeable sunburn from sitting under an umbrella in the grass in the middle of the day (sunny or cloudy) after just 35 minutes.
But while there’s no question that shade isn’t perfect, the sunscreen advantage the study found might not completely translate to real life. For one thing, the sunscreen group slathered on an average of 16 grams of sunscreen to start and 30 grams in total over the afternoon. That’s one-third of the bottle, more than many people use.
And while both groups were allowed to leave the beach for up to 30 minutes during the four-hour period, they did so at different rates: 28 of the umbrella group left, after covering up, for an average of seven minutes, and 30 sunscreeners did for an average of 11 minutes. The researchers don’t say where people went, but if they escaped to deep shade, then the sunscreeners had 57 percent more time out of the sun than the umbrella group, accounting for at least part of their apparent extra protection. This isn’t a huge difference, but it might account for some of the difference.
Shade — under a tree, umbrella, or awning — doesn’t provide full protection from the sun, but this study likely exaggerates the real-world superiority of sunscreen.