Why We Sweat
When we work out, our muscles contract, releasing energy that increases our core body temperature, says Susannah Reiner, PhD, an exercise physiologist and an assistant professor of exercise and sport science at Seton Hall University in South Orange, New Jersey. Hot blood is sent to the skin, where fluid gets released through the sweat glands. As sweat evaporates into the air, it lowers the body temperature.
“Sweating is the body’s mechanism to make sure that we don’t overheat,” Dr. Chu explains.
A few factors influence exactly how much we sweat. Higher temperatures — particularly if it’s humid or there’s little breeze, so the sweat doesn’t evaporate as easily — will increase our perspiration rate.
A vigorous workout creates the same effect by increasing our internal body temperature, Chu says.
But even if two people are doing the same workout in the same place, one might sweat more than the other. That’s because genetics play a role. Men also typically sweat more than women, older adults sometimes sweat less, and larger individuals tend to sweat more than smaller ones, Dr. Reiner says.
Heat acclimation also plays a role, and it’s the repeated heat stress of regular exercise, more than fitness itself, that drives the change. People who are acclimated to hot conditions tend to start sweating sooner and sweat more overall, even if their aerobic fitness is no higher than someone else’s.
But it’s not because they’re working harder. “It’s just because their body is better at dissipating heat — it’s basically an adaptation that allows you to prolong exercise so you don’t have to slow down or spend time resting to cool your body off,” Reiner explains.
