What Happens to Your Body After Hours in a Heat Dome

Extreme heat that persists day and night is hard on the human body in a way that short spells of high temperature are not. When a heat dome settles over a region and refuses to move, the body never gets the overnight break it needs to reset. Understanding what happens hour by hour during that kind of sustained heat can make it easier to recognize when a situation has moved from uncomfortable to dangerous.

Stage 1: Your Body Fights Back

In the first hours of heat exposure, the body does what it is designed to do. Heart rate rises slightly, and blood vessels in the skin expand to allow heat to dissipate through the body's surface rather than pool near vital organs. Sweating begins in earnest, which is the body's primary cooling mechanism.

"The first thing that heat does to your body is that your heart rate goes up a little bit. The blood vessels in your skin actually expand and get bigger," says Dr. Allison Edwards, a family physician and medical advisor to Sesame. "Your body can do this for hours to try and regulate temperature."

How many hours depends on the individual. "Too long for one person might be eight hours," she notes. "Too long for another person might be two or three hours in the exact same conditions."