What causes a fever?

When inflammation comes with a body temperature that is elevated above normal, we call it a fever or pyrexia. The change in temperature is not a defect, but an adjustment by the hypothalamus to a new set point. The set point is established in consequence of release of fever-producing factors called pyrogens, whether endogenous or exogenous. Endogenous pyrogens are produced upon stimulation of exogenous agents.

The fever is a response to infectious, toxic or immunologic disease or injury, at least in warm-blooded animals – although cold-blooded animals like lizards often treat themselves similarly by lying in the sun to raise body temperature.

The fever enhances functions of the immune system and phagocytosis. Also, there are a few bacteria and viruses that reproduce more slowly in the heated temperature because of possible interference with uptake of iron.

So, our initial idea of a fever as something to treat may actually be our bodies’ ways of treating themselves to some kind of moderate degree. But antibiotics are a modern intervention that have given us the capacity to thwart the need of suffering through a fever.

Besides, a fever can actually cause damage itself as in the brain or in pregnancy. The excess heat can cause hyperthermia that creates cranial pressure or can harm a fetus, respectively.

Antipyretic therapy, such as with acetylsalicylic acid, is the way to go. They inhibit prostaglandin production in they hypothalamus, which results in a block of the set point elevation and returns temperature to a normal level.

But children with flu or measles shouldn’t take acetylsalicylic acid because of association with Reyes syndrome, so ibuprofen or something else should be used for children.


Nowak TJ, Hanfod AG. Pathophysiology: Concepts and applications for health care professionals, 3rd ed. 2004. New York, McGraw-Hill.

Published by David Despain, MS, CFS

David is a science and health writer living on Long Island, New York. He's written for a variety of publications including Scientific American, Outside Online, the American Society for Nutrition's (ASN) Nutrition Notes Daily, and Institute of Food Technologists' (IFT) Food Technology magazine and Live! blog. He's also covered new findings reported at scientific meetings including Experimental Biology, AAAS, AOCS, CASW, Sigma Xi, IFT, and others on his personal blog "Evolving Health." David is also an active member of organizations including the National Association of Science Writers (NASW), the American Association for the Advancement of Science (AAAS), the American Society for Nutrition, the Institute of Food Technologists, and the National Audubon Society. David has a master's degree in human nutrition from the University of Bridgeport, and a bachelor's degree in English from University of Illinois at Springfield. He also earned his Certified Food Scientist credential from the Institute of Food Technologists.

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