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When it's hot outside, turn on the fan -- but under these conditions

When the air is hot and humid, researchers found a fan might be beneficial.

ST. PETERSBURG, Fla. — Are you a fan of fans? Consider this when thinking of a sure-fire way to stay cool.

A professor at the University of Sydney wanted to put to the test a warning from the U.S. Centers for Disease Control and Prevention, saying that fans don't help to protect people from heat-related illnesses once temperatures reach into the high 90s. 

The U.S. Environmental Protection Agency also notes people shouldn't use fans when the heat index -- a "feels like" value that considers air temperature and humidity -- is 99 degrees or greater.

Time Magazine reported the professor's study pulled together 12 healthy men and subjected them to varying conditions, including dry heat with a heat index of 115 degrees and humid heat with a heat index of 133 degrees.

Using a fan in an attempt to cool the men down, researchers found the fans more effective at lowering the body's temperature under the higher heat index temperatures. And it's all science: People who sweat (and that's just about everyone) cool off when air flows across the skin through the process of evaporation, and fans help to increase that process.

Hotter and drier air causes the body to warm up, much like a convection oven, said Ollie Jay, an associate professor of health sciences.

“It’s how a convection oven works,” Jay said in Time. “A turkey cooks faster if the fan is on because you’re adding heat by convection faster.” 

RELATED: Europe's record July heat wave intensified by climate change, scientists say

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The best bet to stay cool, especially in drier parts of the county, is to seek air conditioning.

"Fans can help you feel cooler as it blows air over the sweat on your body, evaporating some of it and making that small area near your skin cooler," 10News Chief Meteorologist Bobby Deskins said. "The problem occurs when the temperatures are above 90. It may make you feel slightly cooler, but your body is still surrounded by 90 plus degree air.

"That air can only be cooled so much by evaporation of sweat on your skin."

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