Don’t count on an electric fan to cool you off on extremely hot days; using one may even be detrimental. Fans work by moving air over your skin. This makes sweat evaporate faster (which has a cooling effect) and speeds direct heat transfer between the body and the air (like blowing on hot soup). But the higher the humidity, the less effective evaporation is; and the higher the air temperature, the less heat is dissipated directly into the air.
At air temperatures above skin temperature (about 95°F), fans may actually contribute to heat gain, because the direction of the heat transfer reverses (air to body instead of body to air).
If it’s very hot out and you don’t have air conditioning, you should take cool showers or baths to reduce the risk of heat-related illness, the CDC advises. A recent study found that wearing a water-soaked T-shirt lowered sweat losses and reduced heat strain (but not when combined with a fan). If air conditioning is not available in your home, you can seek out an air-conditioned place that may be open, such as a shopping mall, even if for just a few hours. During heat waves, your local community may open cooling centers.
Whether you use air conditioning, fans, or some combination, it’s also important to drink plenty of water and other nonalcoholic fluids in hot weather to help keep your core body temperature down.
This article first appeared in the UC Berkeley Wellness Letter.
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