Kevin Miller can get a person to the brink of heat stroke in 30 minutes.

In a chamber with a temperature of around 100 degrees, he starts them out on the treadmill, switching off between three minutes of walking and two minutes at an all-out sprint. Soon, they’re breathing faster, their blood vessels are dilating and their heart is working overtime to pump much more blood than usual through their body, fighting to get oxygen to their muscles and organs.

In Miller’s lab, these participants are safe: He brings them close to the heat-stroke threshold of a 105-degree core body temperature in the name of science, to test the efficacy of different treatments.

Heat is the No. 1 weather-related cause of death worldwide and in the United States. Miller is one of the many researchers globally who are expanding our understanding of what heat does to the body and how to counteract its effects. Recently, his Texas State University lab has had success cooling participants using a body bag full of ice—a tactic that is affordable and transportable for emergency responders. Rapid cooling is life-saving medicine.

But heat’s impacts aren’t limited to these obvious moments of emergency. It has a bearing on nearly every aspect of human health, from our skin down to our DNA.

That means long-term exposure to high temperatures—increasingly common as the Earth warms—is causing cumulative harm to our bodies and minds.