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How is body temperature regulated and what is fever?

Created: ; Last Update: November 17, 2016; Next update: 2019.

A healthy body functions best at an internal temperature of about 37°C (98.6°F). But everyone has their own individual "normal" body temperature, which may be slightly higher or lower. Our bodies also constantly adapt their temperature to environmental conditions. It goes up when we exercise, for instance. And it is lower at night, and higher in the afternoon than in the morning.

Our internal body temperature is regulated by a part of our brain called the hypothalamus. The hypothalamus checks our current temperature and compares it with the normal temperature of about 37°C. If our temperature is too low, the hypothalamus makes sure that the body generates and maintains heat. If, on the other hand, our current body temperature is too high, heat is given off or sweat is produced to cool the skin.

Strictly speaking, body temperature refers to the temperature in the hypothalamus and in the vital internal organs. Because we cannot measure the temperature inside these organs, temperature is taken on parts of the body that are more accessible. But these measurements are always slightly inaccurate.

What causes a fever?

People get a fever when their brain sets the body temperature higher than normal. This may happen as a reaction to germs such as viruses or bacteria, but it can also happen as a reaction to substances that are made by the body, such as prostaglandins. Our body produces prostaglandins to fight off germs.

A body temperature of 38°C (100.4°F) or more is considered to be a fever. Temperatures above 39.5°C (103.1°F) are considered to be a high fever, and very high fever is defined as any temperature above 41°C (105.8°F). A temperature between 37.5°C and 38°C is an elevated body temperature.

The regulation of body temperature doesn't always work perfectly in younger children. Compared to older children and adults, they also sweat less when it is warm, and it takes longer for them to start sweating. That is why they are more likely to react with a fever. Babies and young children have a higher body temperature than older children. This is because their body surface area is larger in relation to their body weight. Their metabolism is more active too. Newborns usually have an average body temperature of 37.5°C.

Sources

  • Andreae. Lexikon der Krankheiten und Untersuchungen. Stuttgart: Thieme; 2008.
  • Hoffbauer G, Schaenzler N. Handbuch Medikamente für Kinder – Medikamente und Wirkstoffe, Risiken und Nebenwirkungen, alternative Behandlungsmöglichkeiten. Reinbek: Rowohlt; 2005.
  • Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J. Harrison’s Principles of internal medicine. New York: McGraw-Hill Companies. 18th ed; 2011.
  • National Collaborating Centre for Women's and Children's Health, National Institute for Health and Care Excellence (NICE). Feverish illness in children: assessment and initial management in children younger than 5 years. May 2013. (NICE Clinical Guideline; CG160).
  • Pschyrembel W. Klinisches Wörterbuch. Berlin: De Gruyter; 2014.
  • Ward MA. Fever in infants and children: Pathophysiology and management. In: UpToDate. March 24, 2016.
  • IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

    Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

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© IQWiG (Institute for Quality and Efficiency in Health Care)
Bookshelf ID: NBK279457

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