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How does a fever work?

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Quick answer

A fever works as the body's deliberate defense: it raises your temperature to fight infection. When your immune system detects invaders, it signals the brain to turn up the body's thermostat, making conditions harder for germs and boosting immune activity.

Step by step

  1. Immune cells release chemicals that signal the brain during infection.
  2. The brain's 'thermostat' (the hypothalamus) raises the set temperature.
  3. You feel cold and shiver as your body heats up to the new target.
  4. Higher temperature slows many germs and speeds immune defenses.
  5. Very high or prolonged fevers can be dangerous and need care.

People also ask

Why does the body raise its temperature during illness?
Higher heat hampers many bacteria and viruses while making immune cells work faster, so a moderate fever is part of fighting infection.
Why do you shiver when a fever starts?
Your brain has set a higher target temperature, so you feel cold until you reach it; shivering generates heat to get there.
When is a fever dangerous?
Very high temperatures, fevers in infants, or fevers that persist can signal serious illness and warrant medical attention.

Part of the guide: How Your Body Works →