If you don’t have air conditioning, your first instinct when the heat hits is probably to turn on a fan. But fans don’t always cool you off—it depends whether you’re in a humid or a dry place.
Fans work in humid weather because you’re sweating, and the humidity makes it harder for your sweat to evaporate into the air. Get a cool breeze blowing over your skin—or even the same temperature air, just moving a little faster thanks to the fan—and that sweat will dry out, cooling you in the process.
But if it’s a dry heat, the fan isn’t going to help, and might hurt. Your sweat is already evaporating, after all. A recent study published in the Annals of Internal Medicine found that in dry heat, a fan can make you less comfortable, and even potentially put you at higher risk of overheating. Basically, on a hot and dry day, the fan is just blowing more hot air over your body.
If you already live in a hot, dry place, this advice may not be groundbreaking. But for those of us accustomed to more humid climes, it’s helpful to know that if we’re traveling—or if we’re blessed with a sudden dry day—that other methods of cooling down can be preferable to a fan.
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