Re: why does body temperature increase when someone is ill?

Date: Tue Jun 30 17:19:56 1998
Posted By: George C. Fogg, M.D./Ph.D., Pediatrics, Washington University Medical School
Area of science: Medicine
ID: 899193799.Me

Message:

MadSci Network: Medicine

Dear Rob,
Why do we have fevers and what is the mechanism of increased body temperature? Interestingly, fever seems to be rather old from an evolutionary standpoint. Fish with infections will seek warmer water and reptiles with infections will sun themselves to a greater extent to achieve a higher body temperature.& nbsp; However, let's first go over how fevers are produced in humans.
Increased body temperature is usually induced by some sort of infection, but can be seen with toxin ingestion, malignancy, drug reactions and autoimmune conditions. What is normal body temperature? We generally define 37 degrees C (98.6 degrees F) as normal body temperature based on observations made by Wunderlich over 120 years ago. In fact, our body temperature is not constant and is generally lower in the morning and higher in the early evening. In women, body temperature is slightly lower during ovulation. Therefore, physicians have arbitrarily set 38.3 degrees C as the cutoff point of when they start to get concerned about one's body temperature. Fevers are induced by substances called pyrogens which can be endogenous or exogenous. Although most bacteria have toxins that directly activate the body's central thermoregulatory areas in the brain, they also induce the body to produce endogenous pyrogens as a normal part of the immune response. When the body responds to an infection it produces substances called cytokines which activates the immune system to fight off the infection. Some of these cytokines (interleukin-1 alpha and beta, tumor necrosis factor alpha and beta, interferon alpha and interleukin-6) also signal the anterior hypothalamus (the brain's thermostat) to produce more prostaglandin E2 (PGE2). Elevated PGE2 cause the body to increase both heat production and heat conservation mechanisms which results in the elevation of the core body temperature. Medications for fever (aspirin, acetaminophen (Tylenol), and ibuprofen (Motrin)) all work by inhibiting the production of PGE2. Without PGE2, the temperature set point is not raised and fever is averted. Although all of these drugs work equally well, we generally avoid aspirin in children because of the risk of Reye's Syndrome.
Because cytokines are integral to fever production and the inflammatory response, it would seem reasonable that fever is somehow beneficial to fighting off infections. In fact, at elevated temperatures many microorganisms do not grow as well and white blood cells are slightly more efficient at attacking microorganisms. Unfortunately, elevating the body temperature comes at a cost to the body. Increasing the metabolic rate requires more oxygen consumption, heart rate, glucose utilization and fluid evaporation. Besides it makes you feel very uncomfortable.& nbsp; At temperatures of 40 degrees C dangerous complications such as seizures are quite common especially in young children. Therefore, treating a low grade fever is mainly for symptomatic relief, while a high grade fever (>40 degrees C) should be treated with medications and cool water sponge baths to prevent onset of seizures.
Hope this discussion answers most of your questions.

George Fogg, MD/PhD
St. Louis Children's Hospital
Washington University School of Medicine
St. Louis, Missouri

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