Fans may worsen heat risk when dehydrated

A study cautions that using electric fans in hot, dehydrating conditions may raise the risk of heart problems, prompting new safety guidance.

Heatwave warning shows fans can worsen dehydration and raise heart risk

A University of Sydney study tested 20 adults in a climate chamber set to 39.2 C and 49 percent humidity. Participants completed four three‑hour trials, comparing hydrated and dehydrated states with and without a fan. Researchers measured heart rate, rectal temperature, whole body sweat, thermal discomfort and thirst to see how hydration changes fan effects in extreme heat.

Findings show fan use while dehydrated worsened heart strain and increased sweat losses by about 60 percent. The study notes fans can reduce heat‑related strain only up to about 39 to 40 C; beyond that, fans may worsen heat stress. Lead researcher Connor Graham cautions that in higher heat, turning off fans is the safer option. Public health bodies in the UK have also issued heat warnings as temperatures rise, emphasizing vulnerable groups should take extra care and know heat exhaustion symptoms.

The research adds nuance to a long‑standing debate about cooling strategies in heat waves. It challenges the assumption that fans are universally beneficial, underscoring how hydration status shapes cooling needs. For families and workplaces, the message is not to abandon fans but to pair them with proactive hydration and to adjust cooling methods as temperatures climb. This raises questions for public health messaging and preparedness plans, especially for elderly residents and people with heart conditions.

Highlights

Heat safety is about daily choices, not a single device.