You can fight a fever-but don't kill it

PHOTO (COLOR): Wonder why you feel so bad when you've got a cold or the flu?Blame it on your brain, says Harvard Medical School's Clifford Saper M.D. In an effort to turn up body temperature and kill the bug, he explains, the brain activates the hypothalamus, which acts as the body's thermostat. But the hypothalamus regulates appetite and sleepiness, too, and so these may also get out of whack. In addition, the immune system produces prostaglandin E2, a hormone that helps Infection-fighting cells move into the brain through its protective barrier. But this, too, has an unintended consequence on its way through the brain, postglandin E2 trips chemical switches that leave people feeling drowsy and lethargic. It also acts on pain-sensitive nerves, producing headache and body aches. Aspirin and other pain relievers block the release of prostaglandins, which is why people feel better after taking such agents. But Saper warns that unless the fever is dangerously high, taking aspirin may actually keep the infection around longer. An unchecked fever kills the germ faster and sends a message to the immune system to fight even harder.