https://www.sciencedaily.com/releases/2019/08/190805181627.htm

The research calls into question current guidelines from most public health authorities, including the World Health Organization, that suggest fans may not be beneficial when the temperature rises above 35 degrees Celsius (95°F), as well as recommendations based on heat index caps.

Researchers from the University's Thermal Ergonomics Laboratory simulated heatwave conditions to examine the effect of electric fan use on an individual's core temperature, cardiovascular strain, risk of dehydration and comfort levels.