When your immune system detects harmful microbes, your body raises its internal temperature to create a hostile environment. Turning up the heat suppresses the proliferation of invaders. In short, the fever is the body's way of fighting back. Suppose you catch a virus. The immune system responds by releasing molecules called pyrogens, which induce fever. They signal the brain's hypothalamus to raise the body's set point temperature ' like adjusting a thermostat. When that happens, your muscles contract, causing shivers, and blood vessels constrict to retain heat. You'll feel cold until your body reaches the new set point, often prompting you to add clothes or snuggle into blankets. When the infection subsides, pyrogens decrease and the hypothalamus resets the temperature. You sweat, your blood vessels dilate, and you cool off. You're feeling better. Humans are not special in this regard; all mammals are capable of generating fevers. Even without taking their temperature, you might...
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