Scientific American: Fans May Be Okay for Muggy Days—but Avoid Them in Extreme Dry Heat

Contrary to popular belief, a fan may not be the appliance to use in extreme heat. The U.S. Environmental Protection Agency and the World Health Organization’s Regional Office for Europe have put out similar statements warning that fans will not provide protection against heat related illness in extreme heat above 95 degrees with low humidity. In a recent study, participants saw an increase in dehydration, temperature, and heart rate when using a fan in dry heat and no increase when using a fan in humid heat, even when the heat index was hotter. The cause for this being that fans increase sweat’s evaporation, something that already occurs predominantly in dry heat. Further research is needed to discover exactly when and were fans are appropriate for use and when they are harmful.