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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Human body temperature | 3/4 | https://en.wikipedia.org/wiki/Human_body_temperature | reference | science, encyclopedia | 2026-05-05T07:29:23.993847+00:00 | kb-cron |
Hyperthermia occurs when the body produces or absorbs more heat than it can dissipate. It is usually caused by prolonged exposure to high temperatures. The heat-regulating mechanisms of the body eventually become overwhelmed and unable to deal effectively with the heat, causing the body temperature to climb uncontrollably. Hyperthermia at or above about 40 °C (104 °F) is a life-threatening medical emergency that requires immediate treatment. Common symptoms include headache, confusion, and fatigue. If sweating has resulted in dehydration, then the affected person may have dry, red skin. In a medical setting, mild hyperthermia is commonly called heat exhaustion or heat prostration; severe hyperthermia is called heat stroke. Heatstroke may come on suddenly, but it usually follows the untreated milder stages. Treatment involves cooling and rehydrating the body; fever-reducing drugs are useless for this condition. 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. With fever, the body's core temperature rises to a higher temperature through the action of the part of the brain that controls the body temperature; with hyperthermia, the body temperature is raised without the influence of the heat control centers.
=== Hypothermia ===
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. Symptoms usually appear when the body's core temperature drops by 1–2 °C (1.8–3.6 °F) below normal temperature.
=== 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 in the long term to track ovulation both to aid conception or avoid pregnancy. This process is called fertility awareness.
=== Core temperature === Core temperature, also called core body temperature, is the operating temperature of an organism, specifically in deep structures of the body such as the liver, in comparison to temperatures of peripheral tissues. 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. Temperature examination in the heart, using a catheter, is the traditional gold standard measurement used to estimate core temperature (oral temperature is affected by hot or cold drinks, ambient temperature fluctuations as well as mouth-breathing). Since catheters are highly invasive, the generally accepted alternative for measuring core body temperature is through rectal measurements. Rectal temperature is expected to be approximately 1 °F (0.56 °C) higher than an oral temperature taken on the same person at the same time. Ear thermometers measure temperature from the tympanic membrane using infrared sensors and also aim to measure core body temperature, since the blood supply of this membrane is directly shared with the brain. However, this method of measuring body temperature is not as accurate as rectal measurement and has a low sensitivity for fever, failing to determine three or four out of every ten fever measurements in children. Ear temperature measurement may be acceptable for observing trends in body temperature but is less useful in consistently identifying and diagnosing fever. Until recently, direct measurement of core body temperature required either an ingestible device or surgical insertion of a probe. Therefore, a variety of indirect methods have commonly been used as the preferred alternative to these more accurate albeit more invasive methods. The rectal or vaginal temperature is generally considered to give the most accurate assessment of core body temperature, particularly in hypothermia. In the early 2000s, ingestible thermistors in capsule form were produced, allowing the temperature inside the digestive tract to be transmitted to an external receiver; one study found that these were comparable in accuracy to rectal temperature measurement. More recently, a new method using heat flux sensors have been developed. Several research papers show that its accuracy is similar to the invasive methods.
=== Internal variation === Measurement within the body finds internal variation temperatures as different as 21.5 °C (70.7 °F) for the radial artery and 31.1 °C (88.0 °F) for the brachial artery. It has been observed that "chaos" has been "introduced into physiology by the fictitious assumption of a constant blood temperature".
== Temperature variation ==
=== Hot === 44 °C (111.2 °F) or more – Almost certainly death will occur; however, people have been known to survive up to 46.5 °C (115.7 °F). 43 °C (109.4 °F) – Normally death, or there may be serious brain damage, convulsions, and shock. Cardio-respiratory collapse will likely occur. 42 °C (107.6 °F) – Subject may turn red. They may become comatose, be in severe delirium, and convulsions can occur. 41 °C (105.8 °F) – (Medical emergency) – Fainting, severe headache, dizziness, confusion, hallucinations, delirium, and drowsiness can occur. There may also be palpitations and breathlessness. 40 °C (104 °F) – Fainting, dehydration, weakness, headache, breathlessness, and dizziness may occur as well as profuse sweating. 39 °C (102.2 °F) – Severe sweating, and red. Fast heart rate and breathlessness. There may be exhaustion accompanying this. Children and people with epilepsy may suffer convulsions at this temperature. 38 °C (100.4 °F) – (Classed as hyperthermia if not caused by a fever) – Feeling hot, sweating, feeling thirsty, feeling very uncomfortable. 37.6 °C (99.7 °F) — Classed as a slight fever. May lose appetite, feeling hot, feeling uncomfortable, feeling thirsty.