The Science of Sweat

Here, the verdict on whether sweat releases toxins and proves you’re working out hard, plus answers to other questions about this important body basic.

- Hallie Levine

The fitter I get, the more I sweat. Why is that?

“There are two main reasons. One is that as you improve your fitness, you tend to exercise more intensely, which can make you sweat more,” explains Mary Beth Brown, an assistant professor in the Department of Physical Therapy at Indiana University.

“The other is that you get better at sweating the more you do it.” You’ll start perspiring earlier in your workout, and more of your sweat glands will be activated to help rid your body of excess heat.

But keep in mind sweat isn’t the only measure of how hard you’re working. Some workouts leave you less drenched simply because of the nature of the moves.

“How much you sweat is tied to many factors, including what type of activity you’re doing, your age and your genetics,” says Dr Kory Gill, a sports medicine specialist at the Texas A&M Health Science Center.

A better indicator of your performance is how difficult it is to talk midway through an activity. During a moderate-intensity workout, you should be able to speak in broken sentences; during vigorous exercise, you should be able to manage only a few words at a time.

Why does sweat burn my eyes?

“Sweat contains salt, which can irritate the eyes. Plus, it’s slightly acidic compared with the eye’s fluid,” Mary explains.

Fortunately, there’s no evidence that salt from sweat can harm your eyes, says Dr Stephanie Marioneaux, a spokeswoman for the American Academy of Ophthalmology.

If perspiration is interfering with your workout, wear a sweatband or a moisture wicking hat or visor to trap forehead moisture before it has a chance to creep down into your eyes. Keep artificial tears on hand to use if you do get an errant drop.

Is hot, sweaty yoga really any healthier than regular yoga?