What happens in the body when you get a fever?

When you have a fever, your body is intentionally turning up its internal thermostat as a strategic defense mechanism. Here is how that process works:

• The Signal: When your body detects pathogens—like bacteria or viruses—your immune system releases chemicals called pyrogens. These chemicals travel to the hypothalamus, the part of your brain that acts as your internal thermostat.
• The Reset: The hypothalamus responds by raising your body’s "set point" to a higher temperature. It views this higher temperature as the new baseline for health.
• Creating Heat: Because your brain has decided your body should be warmer than it currently is, you start to feel cold. You may begin to shiver, which is your muscles contracting rapidly to generate heat. Your blood vessels near the skin’s surface may constrict to keep heat inside the core, which is why your skin might feel pale or cold even as your internal temperature climbs.
• The Purpose: A fever is not a disease in itself; it is a tool. By raising the temperature, the body creates an environment that is less hospitable to many invaders, which may struggle to reproduce at higher heat. Additionally, a higher temperature can speed up your immune system's response, helping your white blood cells work more efficiently to clear out the infection.
• The "Break": Once the immune system successfully lowers the level of pyrogens, the hypothalamus resets the temperature back to normal. Your brain then perceives the current heat as "too hot," triggering sweating and vasodilation (widening of blood vessels) to release the excess heat, which is why your fever might "break" with a sudden sweat.

While a low-grade fever is often a healthy sign that your body is fighting off an infection, very high or persistent fevers can put stress on the body and may require medical attention to manage safely.