When you exercise hard in the heat, you expect to sweat. What you might not anticipate? That you’d be covered in salty sweat—actual white salt crystals that stick to your skin or clothing and remain after your sweat has dried.
I first noticed this years ago when my summer long runs began to stretch over the hour mark. When I’d finish my run and start my cool-down walk, sweat would drip into my eyes, causing a serious, screw-my-eyes-shut burn. As my sweat began to dry, my skin would feel tight and gritty, similar to how you feel an hour or so after a dip in the ocean.
Those are two solid hints that my sweat was salty, but it wasn’t until I looked in the mirror pre-shower after one run and saw white crystals clumped along my hairline and traveling down my neck that I thought I might be dealing with actual salt. (I’d noticed the white stuff on my clothing before, but I figured they were just deodorant marks.)
Turns out, being a “salty sweater” is actually pretty common for people who exercise long and in the heat. In fact, in a 2016 study of 157 marathoners published in the Journal of the International Society of Sports Nutrition, researchers determined that nearly 20% of them fit the “salty sweater” criteria based on their higher concentrations of sodium in their sweat.
It made me wonder—is salty sweat actually something to worry about? I touched base with a couple exercise science and hydration experts to find out.
What causes salty sweat?
First, a primer on the importance of sweat—and sodium. Your body’s primary way to regulate its temperature and cool itself down is through evaporation, Riana Pryor, Ph.D., A.T.C, director of the Hydration, Exercise, and Thermoregulation (HEAT) Laboratory at the University at Buffalo tells SELF. When your body’s core temperature gets too hot, it tells its sweat glands to release water to the surface of the skin. It evaporates from there, which allows your body to cool.
But your body doesn’t only release water when you sweat. Your sweat also contains electrolytes like sodium, chloride, and potassium, too. Sodium is an important mineral because it helps maintain fluid balance and nerve function in your body, but it’s also the one lost in the greatest concentration when you sweat.
When you sweat, your body pulls sodium from your bloodstream along with extra water to your sweat glands, so you’re sweating out sodium and water together, says Pryor. (If you didn’t sweat out sodium, your cells would have too much sodium in comparison to water, and your body needs a balance to function optimally.) The water in your sweat evaporates from your skin, but the sodium does not.
It’s when your sweat has a higher concentration of sodium that you’re more likely to see it on your skin (or even your clothing) afterward, she says. This can look like white crystals or a fine white powder on your skin, or even white rings on your clothing, which tend to appear on your chest or back.
There are a few things that can make this high-sodium sweat more likely. People tend to experience salty sweat more when they are performing higher-intensity exercise in a hot environment for a longer duration, says Pryor. That’s why you might notice it more on a run than on a brisk walk.
“When you’re exercising outside somewhere hot, your body is going to try to cool itself—it’s going to be releasing a lot of heat, and you’re going to be sweating a lot,” says exercise physiologist Jeff Forsse, Ph.D., director of the Health, Human Performance, and Recreation Research Lab at Baylor University. “The hotter it is, and the more you sweat, the more potential you have to be sweating out a lot more salt from your intracellular fluids.”