Health experts and scientists are advising people to turn off fans when ambient temperatures and humidity reach dangerous levels [1].
This guidance is critical during the current mega-heatwave in Europe, where reliance on fans may inadvertently lead to heat-related illnesses [1, 2].
Fans cool the body by moving air over the skin, which helps evaporate sweat. However, when the air is already too hot and humid, this process fails. In these extreme conditions, the airflow from a fan can actually raise skin temperature [1, 3].
Instead of cooling the person, the fan begins to push hot air onto the body, essentially acting like a convection oven. This process can impede the body's natural ability to dissipate heat [1, 2].
When the environment exceeds a certain threshold of heat and moisture, the risk of overheating increases. Scientists said that continuing to use fans in these scenarios can accelerate the rise of internal body temperature [1, 2].
Experts suggest monitoring local humidity and temperature levels to determine when fans are no longer effective. Once the cooling effect is lost, turning off the device is recommended to prevent further heat accumulation on the skin [1, 3].
“Fans can increase body heat and risk of illness when ambient temperatures and humidity reach critical levels.”
This shift in guidance highlights the limitations of evaporative cooling. When the air is saturated with moisture and high heat, the body's primary cooling mechanism, sweating, becomes ineffective. In such environments, fans no longer provide relief and can instead contribute to hyperthermia by transporting heat toward the body, making air conditioning or external cooling methods necessary for survival.
