Science, 6 November 2024

Climate chamber experiments in older people offer conflicting answers

When is it too hot to use a fan?

Who knew the simple question of when to use an electric fan could generate so much confusion?

During a heat wave, many people seek relief by sitting in front of a fan. But public health agencies warn that if it’s too hot, the blowing air can actually make things worse by acting like a convection oven—and they differ on that threshold. The U.S. Centers for Disease Control and Prevention (CDC) recommends not using a fan at temperatures above 32.2°C. Others, including the city of Phoenix, give higher thresholds, and the World Health Organization (WHO) puts the limit at 40°C.

New research from two different groups of thermal physiologists favors the higher temperature limits, especially in humid weather. But the groups don’t agree on a single temperature threshold. One study, published on 6 November in The New England Journal of Medicine (NEJM), reports that fans can relieve stress on the heart in elderly people in humid conditions at 38°C. The other, published on 17 October in JAMA, concluded there was little additional benefit from using a fan above 35°C.