When it’s any hotter out than about 98 degrees Fahrenheit, it’s pretty tough for the body to cool down. And that’s when we really start to sweat. Our body temperature is 98.6 degrees Fahrenheit. But when it’s 98 degrees outside we’re not comfortable. We think the temperature is nice at about 75 degrees. Why is this?
The reason has to do with how humans have adapted to heat and cold. We’ve evolved in a way that should keep our bodies at a constant temperature of about 98.6 degrees Fahrenheit, no matter how hot or cold it is. All the proteins in our bodies are perfectly suited to this temperature. Some of the body’s proteins would stop working if you had a heatstroke or frostbite.
So it’s important for the body to have strategies to cope with temperature changes in the environment. Normal bodily processes — such as digesting, breathing, and even just moving — generate heat. These processes help keep us warm when it’s cold out. But when it’s hot outside, we still have some heat to spare. One of the main ways we release this heat energy is simply to radiate it into the air. We feel the most comfortable when the heat generated from our bodies is about equal to the heat lost into the air. This is usually the case when it’s about 75 degrees outside.
Humidity plays a role, too. As your sweat evaporates, it cools you down. But if the humidity’s high, it’s harder for the air to absorb this water — which is why a hot and humid day can be unpleasant.