[♩INTRO].

In general, human bodies operate at about 37 degrees Celsius. So you’d think that air that temperature would feel like nothing not cold, not hot, just neutral.

But anyone who’s spent a sunny day at the beach will tell you that’s not the case. In fact, as a species, we prefer temperatures a lot lower than our running body temp, and there are a couple good reasons why that is. Part of the answer is that not every part of your body is the same temperature.

Your core is home to the organs that really need to stay at that magic 37-degree temp. But other parts of your body, like your arms or feet, tend to be a couple of degrees cooler than your core. And your skin is a few degrees cooler than that, typically sitting at around 32 degrees C.

So it makes sense that you’d feel that five degree difference. But that doesn’t fully explain why body-temperature air feels hot after all, 32-degree air is still considered quite warm. And that’s because we’re actually constantly running hot.

You know how your computer gets hot if it’s working really hard and doesn’t have good airflow? Well, your cells overheat doing their daily tasks, too. The metabolic processes in humans give off a lot of heat as a byproduct, so your body is pretty much always looking for ways to get rid of all that excess warmth.

That’s why a cool 18 to 21 degrees C is considered a comfortable room temperature. When your skin is warmer than the surrounding air, heat will be whisked away via convection that is, gaseous molecules in the air are heated by your skin, then flow away, allowing cooler molecules to take their place. But when the air is near the same temperature or warmer than your skin, your body has to work harder to get rid of excess heat.

One way it can do that is to increase blood flow, which raises the temperature of your skin hopefully bringing it above the temperature of the air again. But when that’s not going to cut it, you start sweating, counting on the evaporation of water from your skin to cool things down. If the weather is particularly humid, though, the water vapor in the air slows down the rate of this evaporation because it basically takes up all the room that would have been available for the water molecules from your sweat.

Which is why hot, humid air feels especially stifling. But, I guess, the trade off is that we humans are able to survive even when it’s really cold out. Since our bodies generate heat, a few layers of insulating cloth can keep us cozy and warm even when the weather is super chilly.

Thanks for asking, Alyx Hannigan, and thanks to all of our patrons who voted for this question in our Patreon poll. If you want to ask some cool questions so we can keep making hot science videos, you can head over to patreon.com/scishow and check it out. [♩OUTRO].