An electric fan may feel like a lifesaver during a heat wave, and for the elderly, it may provide some help—but not nearly as much as you might think. A new study finds that while a high-speed fan can slightly lower core body temperature and improve comfort in hot and humid environments, it doesn't completely prevent heat buildup in the body. In extremely hot and dry environments, the use of fans has previously been shown to increase the workload on the heart, and therefore may cause more harm than good.
Researchers from the University of Sydney, Monash University, the University of Adelaide and the Montreal Heart Institute in Australia studied the effects of using an electric fan at different temperatures on 58 people over the age of 60 (average age 68).
In this randomized crossover trial, 27 participants had a history of coronary artery disease and 31 did not. All participants underwent four three-hour heat exposure trials, spaced at least 72 hours apart: using a fan only (airflow approximately 4 m/s), skin moisturization without a fan, and skin moisturization with a fan without any intervention (control group). The fan was placed slightly more than 3 feet (1 meter) from the subject.
In the skin wetting experiment, researchers sprayed warm water on participants' bare skin to simulate sweating. The fans used in the experiments were standard high-speed household floor-standing fans.
Participants were exposed to a room temperature of 100.4 °F (38 °C) and a relative humidity of 60%, which represents high indoor conditions.
The researchers found that using only a fan slightly lowered participants' core body temperature by an average of 0.18 degrees Fahrenheit (0.1 degrees Celsius) compared with no fan or moist skin, suggesting some benefit from using a high-speed electric fan. Additionally, participants sweated more and reported feeling cooler and more comfortable.
Interestingly, using a fan with skin moisturizing did not change core body temperature, although it did make people feel the most comfortable overall. Research shows that moisturizing the skin inhibits the body's natural perspiration response, thereby reducing the body's heat loss.
Even though people reported feeling slightly more comfortable than during control heat exposure, skin moisturizing alone did not alter core body temperature.
However, when the temperature and humidity changed, the results were completely opposite.考虑到冠状动脉疾病患者存在心脏问题的风险，只有31名健康受试者参与了风扇实验（其余27名受试者仅接受了皮肤润湿/无皮肤润湿的实验）。
他们发现，在炎热干燥的环境中——温度为 45 摄氏度（113 华氏度），湿度为 15%——仅使用风扇实际上会使核心体温升高 0.3 摄氏度（0.5 华氏度），相比完全不使用风扇，这表明风扇实际上将热量带入体内。 Neither skin wetting test demonstrated a significant effect on cooling the subjects.
人们还报告说，在这次测试中使用风扇时他们感觉更热，这表明随着核心温度的上升，他们的舒适度反映了内部的变化。
Overall, research shows that it's not just the temperature number but the amount of moisture in the air that determines how effective a high-speed electric fan is at actually cooling the body.
The link between high temperatures and cardiovascular disease is well established, with overwhelming evidence showing that high temperatures place a greater strain on the heart. Research shows the risk of heart-related death triples when temperatures rise due to hot weather.
Early research from the University of Sydney and the Montreal Heart Institute found that when temperatures and dry air cause the body to heat up, possible interventions such as moisturizing the skin can counteract the heating effects of fans. However, in this study, the slight decrease in core temperature was not statistically significant, so even if people felt more comfortable, the benefit would be minimal.
Research suggests that fans may not be enough to eliminate health risks during heat waves, and for those without access to air conditioning, other interventions, such as community cooling shelters and more nuanced heat risk warnings, could better protect older adults during extreme weather events.
The research was published in the journal JAMA Network Open.