A fan won't keep you cool in a heatwave unless you stay hydrated

Embargoed until: Publicly released: 2025-08-14 01:00

Australia; NSW

What does this mean?

Jump to: MultimediaAttachmentsExpert Reaction

Using a fan in very hot temperatures won't keep you cool and may put extra strain on your heart if you're not staying hydrated, according to Australian research. Previous research shows fans generally become detrimental to your health once the temperature hits about 39-40°C, and the researchers tested how hydration impacts this by exposing 20 people to three hours of heat at the threshold at which fans stop helping, either well-hydrated or dehydrated. They say only those who were well-hydrated felt any relief from the fan, while only dehydrated participants saw worsened heart strain when the fan was on. Overall, the researchers say heart rate and core temperature were much higher in dehydrated participants, underscoring the importance of hydration in heatwaves.