One review of previous research concluded no evidence currently exists supporting or refuting the use of electric fans during heat waves for mortality and illness.
However, public health guidance typically warns against fan use in hot weather, with some research suggesting that fan use could potentially accelerate body heating, researchers said.
Sweat evaporation declines with increasing humidity, so in more humid environments fans may not prevent heat induced elevations in cardiovascular and thermal (core temperature) strain.
Each temperature was tested with and without an 18-inch fan facing the participant (from about 3 feet).
Heart rate and core temperature of the study participants were measured throughout.
Researchers found that the electric fans prevented heat-related elevations in heart and core temperature up to approximately 80 percent relative humidity at 36 degrees Celsius and 50 percent relative humidity at 42 degrees Celsius.
"Thus, contrary to existing guidance, fans may be effective cooling devices for those without air conditioning during hot and humid periods," researchers said.
"Advice to the public to stop using fans during heat waves may need to be re-evaluated," they said.     

The study was published in the journal JAMA.

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