A new study warns that using an electric fan in extremely hot conditions could increase the risk of a deadly heart attack, especially if you are dehydrated.
Researchers from the University of Sydney studied 20 participants in a climate chamber set to 39.2°C with 49% humidity, measuring heart rate, body temperature, sweating, and comfort. Each participant completed four three-hour trials—two while properly hydrated and two while dehydrated—with and without a fan.
The study, published in the journal Emergency Medicine, found that fan use while dehydrated worsened heart strain and increased sweat loss by about 60%, potentially putting users at serious risk. Lead researcher Dr. Connor Graham explained that fans are safe at temperatures up to around 39–40°C, but in hotter conditions, they can actually make heat stress worse because the body heats faster than it can cool itself through sweating.
Fans are most effective when temperatures are below 39°C for healthy adults under 40, and below 38°C for older adults over 65. Vulnerable individuals, such as those taking certain medications like oxybutynin, should be particularly cautious.
The warning comes as the UK experiences soaring temperatures, prompting amber heat-health alerts across five regions. Health officials advise keeping homes cool by closing windows and curtains in sun-facing rooms, staying hydrated, and monitoring for heat-related illness.
Symptoms of heat exhaustion include tiredness, high temperature, excessive sweating, weakness, and thirst. If untreated, it can escalate to heat stroke, which may cause dangerously high body temperatures, organ damage, rapid heartbeat, confusion, seizures, or even loss of consciousness. In such cases, emergency help should be sought immediately.
