FEVER

Fever (also known as pyrexia, from the Greek pyretos meaning fire, or a febrile response, from the Latin word febris, meaning fever, and archaically known as ague) is a frequent medical sign that describes an increase in internal body temperature to levels above normal. Fever is most accurately characterized as a temporary elevation in the body's thermoregulatory set-point, usually by about 1–2 °C (1.8-3.6 °F).

Fever is caused by an elevation in the thermoregulatory set-point, causing typical body temperature (generally and problematically considered to be 37 °C or 98.6 °F) to rise, and effector mechanisms are enacted as a result. A feverish individual has a general feeling of cold despite an increased body temperature, and increases in heart rate, muscle tone and shivering, all of which are caused by the body's attempts to counteract the newly perceived hypothermia and reach the new thermoregulatory set-point.

Fever differs from hyperthermia in that hyperthermia is an increase in body temperature over the body's thermoregulatory set-point, due to excessive heat production or insufficient thermoregulation, or both.

A fever is considered one of the body's immune mechanisms to attempt a neutralization of a perceived threat inside the body, be it bacterial or viral.

Type

Fever classification

	Temperature in rectum, vagina, or ear (core temp.)		Temperature in mouth (oral temp.)		Temperature under the arm (axillary temp.)
Grade	°C	°F	°C	°F	°C	°F
low grade	38-39	100.0-102.2	37.2-38.2	99-100.8	36.8-37.8	98.4-100.2
moderate	39-40	102.2-104.0	38.2-39.2	100.8-102.6	37.8-38.8	100.2-102
high-grade	40-41.1	104.0-106.0	39.2-40.3	102.6-104.6	38.8-39.9	102-104
hyperpyrexia	>41.1	>106.0	>40.3	>104.6	>39.9	>104

The last is a medical emergency because it approaches the upper limit compatible with human life.^{[citation needed]} The ranges differ because normal body temperature differs depending on where it is measured.

Usefulness of fever
Theoretically, fever can aid in host defense.^[8] There are certainly some important immunological reactions that are sped up by temperature, and some pathogens with strict temperature preferences could be hindered.^[13] Fevers may be useful to some extent since they allow the body to reach high temperatures, causing an unbearable environment for some pathogens. White blood cells also rapidly proliferate due to the suitable environment and can also help fight off the harmful pathogens and microbes that invaded the body