Heat exhaustion and heat stroke among active component members of the U.S. Armed Forces, 2020-2024.

In 2024, the crude incidence rates of heat stroke and heat exhaustion were 36.4 and 183.9 cases per 100,000 person-years, respectively. After a period of decline in rates of incident heat stroke from 2020 through 2023, during the 2024 surveillance period an increase was observed. When considering only heat exhaustion, incident rates increased each year during the 5-year surveillance period, from 2020 through 2024. In 2024, higher rates of heat stroke were observed among male service members, when compared to their female counterparts, as well as among non-Hispanic White service members compared to service members of other races and ethnicities. Female service members and non-Hispanic Black service members experienced higher rates of heat exhaustion than their male counterparts and service members of other races and ethnicities, respectively. Heat illness rates were also higher among those younger than age 20 years, Marine Corps and Army service members, and recruit trainees. To mitigate the personal and organizational impacts of heat illness, leaders, training cadres, and supporting medical and safety personnel must inform both their subordinate and supported service members of heat illness risks, preventive measures, early signs and symptoms of illness, and appropriate interventions. In 2024, the crude annual incidence rate of heat stroke increased 16.5%, following a 4-year decrease of 10.8% from 2020 to 2023. All services, apart from the Space Force and Coast Guard, had a higher rate of heat stroke in 2024 than in 2023. The crude annual incidence rate of heat exhaustion increased 52.3% from 2020 to 2024, with incremental increases annually. Increased rates of heat exhaustion in 2024 from 2023 were observed in the Army, Marine Corps, and Coast Guard.