Taking Your Temperature

Taking your temperature is a really funny way to say it. If I take your temperature, it’s not as though I’ve now captured the temperature you previously had, so I’m now sick with whatever has previously ailed you.

I can even take my own temperature, but I do have to put forth some effort to acquire the information. Why should it work, though? Why does measuring your temperature tell you whether or not you’re sick (at least a lot of the time)?

It all starts when your immune system detects something that doesn’t have any real business inside your body—a pathogen. This could be a virus like the flu or covid, or it might be bacteria like food poisoning.

Your immune cells release something called pyrogens. These are complex molecules that operate as little text messages whenever one of those pathogens starts partying a little too hard in there. They signal the brain’s hypothalamus to turn the temperature up inside.

Side note: pyro = fire; gen = create. It’s tough to imagine a more appropriate name.

The hypothalamus induces blood vessels in your body that are close to the skin to constrict, which helps you keep your heat in. At the same time, your metabolism goes up, which can cause you to shiver—and to generate even more heat.

This is a bit of a case of “what’s bad for the goose is also bad for the gander”, since your hypothalamus is deliberately (in the sense that an organ can be deliberate) outside of your normal, healthy range. Pathogens in the human body, after all, tend to do best when the conditions are… well, human.

A higher temperature also helps in another way: the white blood cells in the blood can move around a bit faster in the higher temperature, so your immune response can be boosted by a fever in that way.

It’s pretty common to think that an infection causes a fever, but that’s not quite right. In fact, your own body causes the fever by releasing those pyrogens, at least most of the time, in order to deal with that pesky pathogen.

Pyrogens don’t always play a role, though. If you’re in a very hot place, your body can start to break down, as

Mike Sowden

describes very well here. Medication and certain medical conditions might also cause you to have a fever, but those are less common.

It’s probably not much of a silver lining, but the next time you’re sick, it might make the experience slightly less awful if you can imagine what’s going on inside your body. Even if your immune system isn’t tip-top, there are still trillions of cells at play here, and there are command centers in this war on terrible pathogens.

Your hypothalamus uses the strategy to punish the enemy by cooking them. Army medical units (white blood cells) fly around in there rapidly, helping wounded soldiers to survive and continue the fight.

Thinking about the wonders inside your own body can’t fix you when you’re sick, but maybe it can make you feel just a little bit better.

If you want to read more about tiny intruders inside your body, I wrote a piece you might be interested in next: