If you swim in the great outdoors or in a backyard pool on a hot summer day and put on sunscreen, don’t assume this completely protects you from the sun. Sunburns are actually a quite common consequence of summertime swimming. Here’s why.
For one, water reflects a certain amount of the sun’s ultraviolet (UV) rays, so if your head and neck are above water, the effects of the sun will be even stronger than on land. The rest of the rays penetrate the water, scattering and being absorbed by the water with increasing depth. How much UV light gets reflected and how deep the rest penetrates depends on a number of factors, including the clarity, turbidity, color, and composition of the water as well as the sun’s angle. When you’re underwater, the parts of your body closer to the surface are at higher risk of sunburn, but you would have to go quite deep to avoid any significant exposure to UV light.
You may also stay out in the sun longer than you would on land since the water is cooling—you may not even realize you are getting burned. And you may get a false sense of security when you apply sunscreen. When properly applied, sunscreens that are “water resistant” or “sweat-proof” retain their stated SPF for 40 or 80 minutes, depending on the product—but no sunscreens are really “waterproof.” If you swim outdoors regularly, it’s best to wear a rash guard—a close-fitting top made of spandex and other synthetic fibers often used by surfers. This provides protection not just against abrasion (and hence rashes) but also against the sun. Another option is “UV swimwear” with built-in SPF protection, including long-sleeve tank suits and swim tights, as well as UV-protective bathing caps.
Keep in mind that you can also get sunburned while swimming on an overcast or hazy day, since the UV rays may still be able to penetrate. Thin clouds, in fact, offer little protection and can even increase your UV exposure because of the scattering of light these clouds cause.
This article first appeared in the UC Berkeley Wellness Letter.
Also see Sunscreen Myths and Facts.