Normal human body temperature
Normal human body temperature is a concept that depends upon the place in the body at which the measurement is made. The value of 36.8 °C ±0.7 °C, or 98.2 °F ±1.3 °F is the common oral measurement.[1] Rectal measurements, or measurements taken directly inside the body cavity, are typically about a half degree Celsius (1 °F) higher. The core body temperature of an individual also tends to vary during the day and with activity level, with the lowest value in the second half of the sleep cycle; this low point, called nadir, is one of the primary markers for circadian rhythms.
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History
In 1861, Carl Reinhold August Wunderlich claimed to measure the temperatures of one million people, and reported the average to be 37 °C.[2] In the United States, normal human body temperature is commonly quoted as 98.6 °F, which is an inappropriately exact conversion of Wunderlich's 19th century announcement that the human body temperature is 37 °C.[1] In Russia, the commonly quoted value is 36.6 °C (97.9 °F), based on an armpit reading.
Modern information
The temperature reading depends on which part of the body is being measured. Measurements are commonly taken in the mouth, the ear, the anus, or the armpit. In females, the vagina can also be used. The median daytime temperature among healthy adults are as follows:
- Temperature in the anus (rectum/rectal), vagina, or in the ear (otic) is about 36.3 °C (97.3°F)
- Temperature in the mouth (oral) is about 36.8 °C (98.2 °F)
- Temperature under the arm (axillary) is about 36.5 °C (97.7 °F)
Normal human body temperature varies slightly from person to person and by the time of day. Consequently, each type of measurement has a range of normal temperatures. The range for normal human body temperatures, taken orally, is 36.8±0.7 °C (98.2±1.3 °F). This means that any oral temperature between 36.1 and 37.5 °C (96.9 and 99.5 °F) is likely to be normal.
Variations
Normal body temperature may differ as much as 1.0 °F between individuals or from day to day.
Body temperature normally fluctuates over the day, with the lowest levels around 4 a.m. and the highest around 6 p.m.[3] (assuming the person sleeps at night and stays awake during the day). Therefore, an oral temperature of 37.2 °C (99.0 °F) would, strictly speaking, be normal in the afternoon but not in the morning.
Temperature is increased after eating, and psychological factors also influence body temperature.
Many outside factors affect the measured temperature as well. "Normal" values are generally given for an otherwise healthy, non-fasting adult, dressed comfortably, indoors, in a room that is kept at a normal room temperature (22.7 to 24.4°C or 73 to 76 °F) , during the morning, but not shortly after arising from sleep. Furthermore, for oral temperatures, the subject must not have eaten, drunk, or smoked anything in at least the previous fifteen to twenty minutes, as the temperature of the food, drink, or smoke can dramatically affect the reading.
Children develop higher temperatures with activities like playing, but this is not fever because their set-point is normal. Elderly patients may have a decreased ability to generate body heat during a fever, so even a low-grade fever can have serious underlying causes in geriatrics.
Basal body temperature
Basal body temperature is the lowest temperature attained by the body during rest (usually during sleep). It is generally measured immediately after awakening and before any physical activity has been undertaken, although the temperature measured at that time is somewhat higher than the true basal body temperature. In women, temperature differs at various points in the menstrual cycle, and this can be used for family planning.
Fever
A temperature setpoint is the level that the body attempts to maintains its temperature at. When the setpoint is raised, the result is a fever. Most fevers are caused by infectious disease.
References
- ^ a b Elert, Glenn (2005). "Temperature of a Healthy Human (Body Temperature)". The Physics Factbook. Retrieved on 2007-08-22.
- ^ Mackowiak, P. A.; S. S. Wasserman, M. M. Levine (1992-09-23). "A critical appraisal of 98.6 degrees F, the upper limit of the normal body temperature, and other legacies of Carl Reinhold August Wunderlich". JAMA 268 (12): 1578–1580. doi:. http://jama.ama-assn.org/cgi/content/abstract/268/12/1578. Retrieved on 22 August 2007.
- ^ Body Temperature at WebMD