流感病毒侵入体内，发烧一般都不可避免。为什么一感染这样的病毒体温就要升高呢？发烧到底对人体有什么样的影响呢？

 
When your body temperature rises because of an infection, it's called a fever. Fevers are caused by chemicals called pyrogens (热源) lowing in the bloodstream. Pyrogens make their way to the hypothalamus (视丘下部) in the brain, which is in charge of regulating¹ body temperature. When pyrogens bind² to certain receptors in the hypothalamus, body temperature rises.

One common pyrogen is called Interleukin-1 (IL-1, 白细胞间介素). IL-1 is produced by white blood cells called macrophages（巨噬细胞）when they come into contact with certain bacteria and viruses. IL-1 has multiple purposes, one of which is to signal other white blood cells, called helper T cells, into action.

One purpose of a fever is thought to be to raise the body's temperature enough to kill off certain bacteria and viruses sensitive to temperature changes. One interesting debate right now, therefore, is, "Should you lower a fever?" Aspirin³, for example, will reduce fever; but if the fever is actually helping⁴ rid the body of infection, then lowering it might not be a good idea. On the other hand, people sometimes die from fever. Right now the general medical consensus⁵ falls on the "reduce the fever" side of the fence.