Summer is just getting started, and millions of people are under heat advisories^[1] as a major heat wave^[2] spreads across large parts of the central and eastern U.S.^[3] in late June 2025.

For many people, summer is their favorite time of year. However, summer also brings the risk of dangerously high temperatures and humidity.

In the U.S., hundreds of people working or playing outside – even those who seem healthy – ...