Human body temperature
It depends on sex, age, time of day, exertion level, health status (such as illness and menstruation), what part of the body the measurement is taken at, state of consciousness (waking, sleeping, sedated), and emotions.
[8][9] In adults a review of the literature has found a wider range of 33.2–38.2 °C (91.8–100.8 °F) for normal temperatures, depending on the gender and location measured.
[14] Reported values vary depending on how it is measured: oral (under the tongue): 36.8±0.4 °C (98.2±0.72 °F),[15] internal (rectal, vaginal): 37.0 °C (98.6 °F).
A woman's basal body temperature rises sharply after ovulation, as estrogen production decreases and progesterone increases.
Fertility awareness programs use this change to identify when a woman has ovulated to achieve or avoid pregnancy.
[citation needed] It has been found that physically active individuals have larger changes in body temperature throughout the day.
Elderly people may have a decreased ability to generate body heat during a fever, so even a somewhat elevated temperature can indicate a serious underlying cause in geriatrics.
[18] The study's authors believe the most likely explanation for the change is a reduction in inflammation at the population level due to decreased chronic infections and improved hygiene.
[citation needed] Oral temperatures are influenced by drinking, chewing, smoking, and breathing with the mouth open.
[25] Similarly, waking up unusually early, sleeping in, jet lag and changes to shift work schedules may affect body temperature.
This may be done by moving out of direct sunlight to a cooler and shaded environment, drinking water, removing clothing that might keep heat close to the body, or sitting in front of a fan.
Bathing in tepid or cool water, or even just washing the face and other exposed areas of the skin, can be helpful.
In hypothermia, body temperature drops below that required for normal metabolism and bodily functions.
In humans, this is usually due to excessive exposure to cold air or water, but it can be deliberately induced as a medical treatment.
In women, temperature differs at various points in the menstrual cycle, and this can be used in the long term to track ovulation both to aid conception or avoid pregnancy.
Core temperature is normally maintained within a narrow range so that essential enzymatic reactions can occur.
Significant core temperature elevation (hyperthermia) or depression (hypothermia) over more than a brief period of time is fatal.
Until recently, direct measurement of core body temperature required either an ingestible device or surgical insertion of a probe.
[32] There are non-verbal corporal cues that can hint at an individual experiencing a low body temperature, which can be used for those with dysphasia or infants.
[37] Examples of non-verbal cues of coldness include stillness and being lethargic, unusual paleness of skin among light-skinned people, and, among males, shrinkage, and contraction of the scrotum.
[38] Environmental conditions, primarily temperature and humidity, affect the ability of the mammalian body to thermoregulate.
A 2022 study on the effect of heat on young people found that the critical wet-bulb temperature at which heat stress can no longer be compensated, Twb,crit, in young, healthy adults performing tasks at modest metabolic rates mimicking basic activities of daily life was much lower than the 35 °C (95 °F) usually assumed, at about 30.55 °C (86.99 °F) in 36–40 °C (97–104 °F) humid environments, but progressively decreased in hotter, dry ambient environments.
In the 19th century, most books quoted "blood heat" as 98 °F, until a study published the mean (but not the variance) of a large sample as 36.88 °C (98.38 °F).
The 37 °C value was set by German physician Carl Reinhold August Wunderlich in his 1868 book,[44] which put temperature charts into widespread clinical use.
