Fans may increase heat discomfort in older adults during dry, hot conditions

Research led by the Montreal Heart Institute has discovered that electric fans can raise core temperatures and increase discomfort for older adults at 45 °C with 15% relative humidity. However, fan use at 38 °C and 60% relative humidity resulted in a slight decrease in core temperature and greater comfort.

The CDC warns against using fans above 32 °C due to concerns that increased airflow might accelerate heat gain among vulnerable populations. Previous modeling studies and small laboratory trials suggested that airflow could be beneficial in high humidity, but effects on elderly individuals at very high temperatures remained uncertain. There is a pressing need for practical, affordable cooling solutions for older adults facing elevated heat-related health risks.

In the study "Thermal and Perceptual Responses of Older Adults With Fan Use in Heat Extremes," published in JAMA Network Open, researchers conducted a secondary analysis of a randomized crossover clinical trial examining how fan use and skin wetting affect core temperature, sweating, and thermal perception during extreme heat exposures.

A total of 58 elderly participants (average age 68 ± 7 years), including 27 with coronary artery disease, underwent 320 laboratory heat sessions. Each session lasted three hours in a climate chamber set at either 38 °C and 60% relative humidity or 45 °C and 15% relative humidity.

The humid condition trials included four randomized scenarios: control, fan only, skin wetting only, and combined fan plus skin wetting, separated by at least 72 hours.

During the very hot, dry sessions (45 °C at 15% humidity), participants with coronary artery disease were limited to control and skin-wetting scenarios. The measurements tracked included rectal temperature, pre- and post-body mass for calculating sweat rate, thermal sensation on a seven-point scale, and comfort on a four-point scale.

In the humid chamber (38 °C at 60% RH), fan use decreased rectal temperature by −0.1°C, increased sweat rate by 57 mL/h, improved thermal sensation by −0.6 arbitrary units (AU) using an ASHRAE 7-point scale, and enhanced comfort by −0.6 AU. Skin wetting alone reduced sweat loss by 67 mL/h, enhancing perception of ease; combining both strategies produced maximum perceptual benefits: thermal sensation −1.1 AU, comfort −0.7 AU, without altering core temperature.

In the dry chamber (45 °C at 15% RH), fan use increased core temperature by 0.3°C, boosted sweating by 270 mL/h, and worsened sensation and comfort both by 0.5 AU each. Skin wetting alone decreased sweating by 121 mL/h but improved thermal sensation by −0.4 AU with no change in comfort.

The researchers conclude that electric fans can serve as a safe, low-cost cooling option for older adults during hot and humid weather at 38 °C, but should be avoided in very hot, dry conditions. Simple skin wetting provides an additional method to manage heat stress while reducing dehydration risks. Public health agencies may use these findings to refine summer heat-safety messages targeted at the elderly.

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