The US Centers for Disease Control and Prevention (CDC) advise against fan use above 32 °C (ie, 90 °F) because it can increase body temperature.1 Modeling suggests fans reduce body temperature up to 37 to 39 °C (ie, 99 to 102 °F), depending upon humidity.2 In humid heat, fan use reduced body temperature in young adults at 42 °C (ie, 108 °F),3 or healthy older adults at 36 °C (ie, 97 °F).4 Above 36 °C, fan use effects on older adults remain unclear but is likely detrimental at 42 °C or hotter.5 We reported that fan use with and without skin wetting reduces cardiac strain of older adults in hot and humid heat but tripled cardiac strain in very hot and dry heat.6 Here, we report the results for body temperature, sweating, and thermal perceptions.
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https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2836908
2 Medical News 