What Physically Causes a Fever?

When you get a cold or some other ailment a fever is a typical symptom. So what is your body doing “wrong” to make your temperature go up? I guess more generally what does your body do to maintain the correct 98.6 F body temp?

I’ll give you the dummy, 9th-grade-biology answer. Then someone else can come along and give the more scientific one :slight_smile:

Your body is working to fight infection. Since that work produces heat (like most work - feel your computer sometime, or your TV) the body heats up above normal temperature to give you a “fever.”

If you’ve ever gotten a cut that ends up with an infection, you’ll notice the area gets warmer than the rest of you. It’s because your body is fighting infection in that area. Just happens to be on the outside, not inside like the flu.

Your metabolism is what keeps your body at 98.6. The processes that happen in your body that keep it alive produce heat. Other animals have different body temperatures because their body processes are different. A symptom of hypothyroidism in humans is lower-than-98.6 body temperature…which is a sign that the metabolism isn’t working right and can’t sustain the heat. And low metabolism can lead to weight gain - that’s why another symptom of hypothyroidism is weight gain.

I quite like the term ‘endogenous pyrogen’, but fever more generally involves a change in the body’s thermoregulatory set-point up in the hypothalamus.

I’ll give the 10th grade answer, which is a few more details, but still probably leaving a whole bunch out.

Basically, your body rarely needs to make you temperature higher. The things you do (eating, moving, digesting food) produce a heck of a lot of heat. Your body’s job is to get rid of excess heat (too hot and you’ll denature your own proteins and “cook” yourself) with getting rid of too much heat (too cold and you’ll lose consciousness and muscle control). Your body gets rid of heat several ways: convection, conduction, perspiration and radiation (really? radiation? I didn’t know that, but both of these sites list radiation). The way your body knows HOW MUCH heat to get rid of is by constantly testing your body temperature with little sensors in the hypothalamus.

No one is entirely certain why you sometimes get a fever when you’re sick. One theory is that the sensors in the hypothalamus are out of commission. Another theory is that the body senses certain pathogens and tries to denature their proteins by “cooking” them and killing them.

A cut gets warm because of increased blood flow - blood brings heat from deep in the body, which is lost at the skin to conduction with the cooler air. I don’t think it’s the same thing with an internal infection - there may be increased blood flow, but if it’s not at the surface, it won’t feel warm to the touch.