  fever (also known as pyrexia or febrile response) is one of the most common medical signs and is characterized by an elevation of body temperature above the normal range of  due to an increase in the temperature regulatory set-point. this increase in set-point triggers increased muscle tone and chills. as a person's temperature increases, there is, in general, a feeling of cold despite an increase in body temperature. once body temperature has increased to the new set-point temperature, there is a feeling of warmth. a rapid decrease in temperature may be accompanied by sweating and feeling hot. a fever can be caused by many medical conditions which range from benign to potentially serious. some studies suggest that fever is useful as a defense mechanism as the body's immune response can be strengthened at higher temperatures; however, there are arguments for and against the usefulness of fever, and the issue is controversial. with the exception of very high temperatures, treatment to reduce fever is often not necessary; however, antipyretic medications can be effective at lowering the temperature, which may improve the affected person's comfort. fever differs from uncontrolled 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.  ==definition==  a wide range for normal temperatures has been found. fever is generally agreed to be present if the elevated temperature is caused by a raised set point and: * temperature in the anus (rectum/rectal) is at or over  * temperature 
Fever