Understanding Fever Better

ID-100166987Fever (rise in body temperature above normal range of 36.5–37.5 °C or 98–100 °F) occurs due to increase in temperature set-point in hypothalamus, triggered by pyrogens. Pyrogens are chemicals that raises body temperature and released due to inflammation, infection or by certain tumors (usually cancerous tumors). Fever is also known as pyrexia. Rise in body temperature (fever) may lead the muscle tone to increase cause shivering.

An individual with fever usually feels cold during fever (when body temperature is raising), despite increase in body temperature and once the body temperature stops raising further, the person with fever feels warmth. Fever can be due to minor cause requiring no medical attention or fever may be manifestation of potentially serious underlying disorder such as cancer or serious infection. There are thoughts of usefulness of fever, although controversies exist on this topic (usefulness of fever). Medication, which help in reducing body temperature are called antipyretics and common antipyretic medications include ibuprofen, paracetamol (acetaminophen), aspirin etc.

What is the definition of fever?

Normal body temperature of an individual varies throughout the day and it is not easy therefore to define fever clearly. There is also variation of body temperature depending on site from where body temperature is measured. Body temperature is commonly measured from axilla, mouth and anus/rectum. Axillary temperature is lower than oral temperature, and oral temperature lower than rectal/anal temperature. The following is usually accepted definition of fever:

  • Axillary temperature (thermometer placed under the arm) of over 37.2 °C or 99.0 °F is fever
  • Oral temperature (thermometer placed under the tongue) of more than 37.7 °C or 99.9 °F is fever
  • Anal/rectal temperature (thermometer placed inside anus into the rectum) of more than 37.5–38.3 °C (99.5–100.9 °F)

Normal body temperature may vary according to various factors such as age, sex, time of the day (body temperature is highest in the evening and lowest in the early morning), physical activity level. Body temperature rises during physical exercise due to generation of excess heat due to muscular activity, which generate large amount of heat energy, but it is not fever, because temperature set point is normal and not raised during exercise. Hence, a raised body temperature above normally acceptable normal limit may not always mean fever. Similarly a frail elderly individual with “normal” body temperature may have fever, because the elderly person may not be able to generate enough body heat and a “normal” body temperature for him may be significant fever clinically. We can comprehensively say that the rise in body temperature to be termed as fever, temperature set point must be raised due to some pathology.

“Image courtesy of tiverylucky / FreeDigitalPhotos.net”.

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