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You're dripping with sweat after a hard-charging workout session—so does all that sweat mean you're burning more calories than usual? It kind of makes sense; perspiring a lot clearly means you're exerting yourself, and that requires extra energy. But does sweating really burn calories? To unpack the science and get answers, we took it to the experts.
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What causes sweating
First, let's get into the purpose of perspiring: Your body sweats not to burn calories but to protect you from overheating. "Sweating is the way in which we cool the body during exercise or other heat stress," Thad E. Wilson, PhD, a professor in the department of physiology at the University of Kentucky College of Medicine, tells Health. (His research focuses on sweat glands and skin blood flow.)
It might be hard to believe—especially when you're deep in a HIIT workout—but exercise itself doesn't stimulate sweating, says Wilson. Rather, exercise triggers an increase in internal temperature, which ultimately tells your body that it's time to sweat to cool down.
More sweat doesn’t mean more calorie burn
Basically, sweating on its own doesn't affect how many calories you burn. True, it does take energy to physically transport the ions that allow for water to move into glands to get secreted as sweat, says Wilson, but not much. In other words, some energy is needed in the process of sweating, but not enough to make a huge difference in the way you feel or what you weigh. Sweat is only an indication that your body has lost water, not body fat, exercise specialist Gabbi Berkow, a certified personal trainer who has her MA in exercise physiology, tells Health.
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Physical activity in general burns calories. The more intensely you use large muscle groups, the more calories your body will utilize—and the more heat (and sweat) your body will generate, says Wilson.
This calorie burn is most significant during an aerobic workout versus a weight-training workout. But if you're doing a weight or interval workout and resting in between sets, you might find that you have to towel off less. "That doesn't mean you didn't get a good workout, burn calories, or build strength—it just means your body temperature didn't rise as much," says Berkow.
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Everyone sweats at different rates
Just because you're sweating so much you could mop the floor while your friend is barely glistening doesn't mean much. "There are huge individual variations in the ability to sweat," says Wilson. If you're acclimated to hot weather, you'll likely sweat more initially because your body knows how to efficiently cool itself. Different people start sweating at different temperatures, too.
Bottom line: How much you sweat is an inaccurate way to measure calorie burn. "Sweating buckets does not necessarily reflect a great workout," says Berkow. "Sweating a lot means your body became very hot from the workout and needs to cool off." Still don't buy it? Here's an experiment: Go out at 2 p.m. in the sun on an unseasonably warm day, and you'll likely sweat more than that same walk in unseasonably cold, dark weather—but you'll burn basically the same amount of calories.
If you really want to know how hard or intense you're working out, monitor your heart rate. That can take some special equipment, like a heart rate monitor, health tracker, or app. If those aren't available to you, then score yourself on the Rate of Perceived Exertion (RPE) scale, suggests Berkow. All you do is rate how difficult the workout is on a 1-10 scale. You won't know exact numbers, but you will be able to compare different workouts and get a sense of when you're taking it easier than usual and when you're killing it.
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