Montreal Heart Institute-led research has found that older adults using an electric fan at 38 °C and 60% relative humidity experienced a modest fall in core temperature and greater comfort. Fan use at 45 °C and 15% relative humidity raised core temperature and increased discomfort.
CDC guidance warns against fan use above 32 °C because of concerns that added airflow could speed heat gain in vulnerable groups. Modeling studies and small laboratory trials have hinted that airflow may help when humidity is high, but effects at very high temperatures in older adults have remained uncertain. Older individuals face elevated heat-related morbidity, creating an urgent need for practical, low-cost cooling ideas.
In the study, “Thermal and Perceptual Responses of Older Adults With Fan Use in Heat Extremes,” published in JAMA Network Open, researchers performed a secondary analysis of a randomized crossover clinical trial to test how fan use and skin wetting influence core temperature, sweating, and thermal perception during extreme-heat exposures.
A cohort of 58 elderly (68 ± 7 years old) community-dwelling participants, including 27 with coronary artery disease, completed 320 laboratory heat exposures. Each spent three hours in a climate chamber set at 38 °C and 60% relative humidity or at 45 °C and 15% relative humidity.
Exposures in the humid trial included four randomized conditions: control, fan alone, skin wetting alone, and combined fan plus skin wetting, separated by at least 72 hours.
During very hot, dry sessions at 45 °C and 15% humidity, participants with coronary artery disease were limited to control and skin-wetting sessions. Rectal temperature, pre- and post-body mass for sweat rate, thermal sensation on a seven-point scale, and comfort on a four-point scale were recorded.
In the humid chamber, fan use lowered rectal temperature by −0.1 °C, raised sweat rate by 57 mL/h, and improved thermal sensation by −0.6 AU (arbitrary units using an ASHRAE 7-point scale) and comfort by −0.6 AU. Skin wetting cut sweat loss by 67 mL/h and eased perceptions, and combining both strategies produced the largest perceptual gains: thermal sensation −1.1 AU, comfort −0.7 AU, without altering core temperature.
In the dry chamber, fan use raised core temperature by 0.3 °C, boosted sweating by 270 mL/h, and worsened sensation and comfort by 0.5 AU each. Skin wetting alone lowered sweating by 121 mL/h and improved sensation by −0.4 AU, with comfort unchanged.
Study investigators conclude that electric fans can serve as a safe, low-cost cooling option for older adults during hot, humid weather at 38 °C, but should be avoided in very hot, dry conditions. Simple skin wetting offers an additional means to manage heat stress while limiting dehydration. Public health agencies may use these findings to refine summer heat-safety messages for seniors.