People are “warm-blooded,” meaning that the human body has ways of maintaining a fairly constant internal body temperature, despite changes in the temperature of the surroundings. One advantage of such temperature regulation is that the muscles are always ready to work. When the body is in cooler air or water, extra heat is produced by shivering. Cooling is accomplished by evaporation of sweat.
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The classic study of human body temperature was published by Carl Wunderlich1 in 1868. In a survey of 25,000 adults, recording temperatures to the nearest degree centigrade, he arrived at an average of 37° centigrade. Later authors converted this figure to degrees Fahrenheit, but added extra, unjustified precision, giving the traditional 98.6°F.
A modern study, carried out in 1991 at the University of Maryland2 with much better instrumentation, found a mean temp of 98.2 degrees Fahrenheit. Average temperatures of individuals varied by as much as 4.8°F, and a healthy individual’s temperature might vary during the course of a day by as much as 1.09°F. The lowest temperatures were at 6 am, and the highest between 4 and 6 pm. Women, on the average were slightly warmer than men (by 0.3°F, 0.2°C). Other studies have found the highest temperatures between 6 and 10 pm, and the lowest between 2 and 4 am.
1. C. Wunderlich.
Das Verhalten der Eigenwarme in Krankheit.
Leipzig: Otto Wigard, 1868.
Phillip A. Mackowiak, Steven S. Wasserman and Myron M. Levine.
A critical appraisal of 98.6°F, the upper limit of the normal body temperature, and other legacies of Carl Reinhold August Wunderlich.
JAMA, volume 268, no. 12, pages 1578-1580 (Sept 23/30, 1992).
Horvath, H. Menduke, G. M. Piersol.
Oral and rectal temperatures of man.
JAMA, volume 144, pages 1562-1565 (1950).
Persons with heat stroke, a life-threatening condition, have reached temperatures as high as 113° F (44.4°C). Heat stroke is a danger to marathon runners, who may reach temperatures as high as 105.8°F (41°C) and recover—or may continue on to heat stroke. A temperature of 106°F (41.1°C, measured rectally) is a medical emergency; treatment of heat stroke is begun by immediately plunging the patient into an ice-water bath.
In children, temperatures of 106°F and above are often accompanied by convulsions. At 108°F, brain damage is common.
Temperatures of 114°F (45.6°C) and above are “incompatible with life.”
C. H. Wyndham.
Heatstroke and hyperthermia in marathon runners.
Annuals of the New York Academy of Science, volume 301, page 128 (1977).
H. B. Simon.
JAMA, volume 236, page 2419 (1976).
Hypothermia begins at temperatures below 95°F (35°C). Humans lose consciousness at about 91°F (32.8°C).
Severe hypothermia begins when body temperature falls below 86°F (30°C). Old people and infants are particularly susceptible: hypothermia has occurred even at room temperatures as high as 60°F. Check the links.
Mark S. Blumberg.
Body Heat. Temperature and Life on Earth.
Cambridge (MA): Harvard University Press, 2002.
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Last revised: 20 August 2004.