The intensification of heat stress poses significant risks to global populations, particularly in subtropical regions. Exposure to extreme heat stress has risen from 16% to 22% of the global population, equivalent to about one billion people. Vulnerable groups, including those with pre-existing health conditions like cardiovascular disease, diabetes, and asthma, are at heightened risk. Nighttime heat stress exacerbates these risks by reducing the body's ability to recover. Regions such as Europe and South America now experience extreme heat stress 2.5 times more often, while North America sees a doubling of such events. The findings underscore the urgent need for adaptive measures to mitigate health impacts.