Why does your body temperature rise when you have a virus such as the flu?

When your body temperature rises because of an infection, it's called a fever. Fevers are caused by chemicals called pyrogens flowing in the bloodstream. Pyrogens make their way to thehypothalamus in the brain, which is in charge of regulating body temperature. When pyrogens bind to certain receptors in the hypothalamus, body temperature rises.

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