If you’ve ever wondered why it can sometimes feel stiflingly hot as your clothes quickly dampen on a summer afternoon, humidity is the likely culprit.
Because of humidity, which is a measure of the air’s water vapor content, the body’s perspiration evaporates from the skin at a much slower rate.
“Evaporation is a cooling process,” said AccuWeather Senior Meteorologist Dave Dombek. “If you step out of the pool or a lake, you get a chill because the air is very dry, and that water almost instantly starts to evaporate off of your skin so that it cools it.”
According to the MIT School of Engineering, the rate at which water or sweat evaporates depends on the level of water currently in the air.
The water-saturated air causes your clothes to feel drenched in sweat, especially while wearing certain fabrics such as cotton, which can soak up and retain moisture.
“It just lays on your skin,” said Dombek. “That’s why you feel much more uncomfortable.”
When sweat can’t evaporate, the body can’t regulate its temperature, according to the National Weather Service (NWS).
In contrast, engaging in physical activity in dry, normal conditions will cause any sweat to evaporate quickly from the skin.
Though arid conditions may feel more comfortable than a sticky, humid day, dry heat can also be more dangerous because you may not realize you’re sweating, Dombek said.
“[When] you’re exerting yourself [by] taking a 10-mile hike or running, you feel great because you don’t have perspiration on your skin, it’s evaporating,” Dombek said.
Meanwhile, the body loses lots of water, increasing the likelihood of dehydration, he said.