Cooling guidance under heat risk

A new Australian study suggests using electric fans during extreme heat, especially when dehydrated, may raise heart strain.

Fans May Increase Heart Risk in Extreme Heat Study

Researchers from the University of Sydney ran a controlled experiment with 20 adults in a climate chamber set to 39.2C and 49% humidity. They tested two hydration states—well hydrated and dehydrated—and both with and without a fan. They tracked heart rate, rectal temperature, whole body sweat rate, thermal discomfort and thirst. The study found that fan use while dehydrated increased sweat losses by about 60% and worsened heart strain, potentially raising the risk of heart attacks. In contrast, fans appeared to reduce heat-related strain at temperatures around 39 to 40C, but the benefit drops as conditions climb higher, the researchers noted. Previous work suggests fans can help below certain thresholds, while hotter conditions call for caution. The lead researcher added that guidance for older adults, and those on certain medications, should reflect these nuances and remain tailored to individual risk.

The findings complicate a common summer habit. Fans are cheap and widely used, especially where air conditioning is scarce. Public messaging that treats fans as universally protective may be misleading. This study underlines the need to pair cooling with hydration and to adjust advice for people with higher heart risk. In a warmer world, practical cooling becomes a balance of comfort, fluid intake and sensible limits on devices. The real test is translating lab results into clear, actionable tips for homes and buildings.

Highlights

Heat safety is a daily practice, not a single device.