5.2 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Human body temperature | 2/4 | https://en.wikipedia.org/wiki/Human_body_temperature | reference | science, encyclopedia | 2026-05-05T07:29:23.993847+00:00 | kb-cron |
=== Natural rhythms === Body temperature normally fluctuates over the day following circadian rhythms, with the lowest levels around 4 a.m. and the highest in the late afternoon, between 4:00 and 6:00 p.m. (assuming the person sleeps at night and stays awake during the day). Therefore, an oral temperature of 37.3 °C (99.1 °F) would, strictly speaking, be a normal, healthy temperature in the afternoon but not in the early morning. An individual's body temperature typically changes by about 0.5 °C (0.9 °F) between its highest and lowest points each day. Body temperature is sensitive to many hormones, so women have a temperature rhythm that varies with the menstrual cycle, called a circamensal rhythm. 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. During the luteal phase of the menstrual cycle, both the lowest and the average temperatures are slightly higher than during other parts of the cycle. However, the amount that the temperature rises during each day is slightly lower than typical, so the highest temperature of the day is not very much higher than usual. Hormonal contraceptives both suppress the circamensal rhythm and raise the typical body temperature by about 0.6 °C (1.1 °F). Temperature also may vary with the change of seasons during each year. This pattern is called a circannual rhythm. Studies of seasonal variations have produced inconsistent results. People living in different climates may have different seasonal patterns. It has been found that physically active individuals have larger changes in body temperature throughout the day. Physically active people have been reported to have lower body temperatures than their less active peers in the early morning and similar or higher body temperatures later in the day. With increased age, both average body temperature and the amount of daily variability in the body temperature tend to decrease. 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. One study suggested that the average body temperature has also decreased since the 1850s. 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.
=== Measurement methods ===
Different methods used for measuring temperature produce different results. The temperature reading depends on which part of the body is being measured. The typical daytime temperatures among healthy adults are as follows:
Temperature in the rectum (rectal), vagina, or in the ear (tympanic) is about 37.5 °C (99.5 °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) Generally, oral, rectal, gut, and core body temperatures, although slightly different, are well-correlated. Oral temperatures are influenced by drinking, chewing, smoking, and breathing with the mouth open. Mouth breathing, cold drinks or food reduce oral temperatures; hot drinks, hot food, chewing, and smoking raise oral temperatures. Each measurement method also has different normal ranges depending on sex.
=== Infrared thermometer ===
As of 2016, reviews of infrared thermometers have found them to be of variable accuracy. This includes tympanic infrared thermometers in children.
=== Variations due to outside factors === Sleep disturbances also affect temperatures. Normally, body temperature drops significantly at a person's normal bedtime and throughout the night. Short-term sleep deprivation produces a higher temperature at night than normal, but long-term sleep deprivation appears to reduce temperatures. Insomnia and poor sleep quality are associated with smaller and later drops in body temperature. Similarly, waking up unusually early, sleeping in, jet lag and changes to shift work schedules may affect body temperature.
== Concept ==
=== Fever ===
A temperature setpoint is the level at which the body attempts to maintain its temperature. When the setpoint is raised, the result is a fever. Most fevers are caused by infectious disease and can be lowered, if desired, with antipyretic medications. An early morning temperature higher than 37.3 °C (99.1 °F) or a late afternoon temperature higher than 37.7 °C (99.9 °F) is normally considered a fever, assuming that the temperature is elevated due to a change in the hypothalamus's setpoint. Lower thresholds are sometimes appropriate for elderly people. The normal daily temperature variation is typically 0.5 °C (0.90 °F), but can be greater among people recovering from a fever. An organism at optimum temperature is considered afebrile, meaning "without fever". If temperature is raised, but the setpoint is not raised, then the result is hyperthermia.
=== Hyperthermia ===