What is Fever?
A '''fever''' is when a person's body temperature is hotter than 37.5 degrees [[Celsius]] (99.5 [[Fahrenheit]]). Normal body temperature for humans varies based on a variety of factors, including age and level of physical activity.<ref>[http://firstaid.webmd.com/body-temperature {{Webarchive|url=https://web.archive.org/web/20130116170722/http://firstaid.webmd.com/body-temperature |date=2013-01-16 }} WebMD Body Temperature</ref> It is typically cited as 37 degrees Celsius (98.6&nbsp;F), but naturally varies from person to person by at least .5 degrees Celsius. The actual [[measurement]] of body [[temperature]] will vary based on the location of the [[measurement]]. For a [[temperature]] taken from under the [[tongue]], the measurement may be lower. [[Rectal]] temperatures will read about 0.3&nbsp;C (0.55&nbsp;F) higher, and armpit temperatures will read about the same amount lower. When people are ill, their body's [[immune system]] fights the [[disease]], and so the body temperature rises. Fever is a defensive measure of the body against the germs: the life cycles of the germs are disrupted when the body temperature rises. About 38&nbsp;°C (100.4&nbsp;F) degrees is called a low-grade fever, and above 39.5&nbsp;°C (103&nbsp;F) degrees is a high-grade fever. [[Child]]ren usually have a higher fever than adults; their [[immune system]] is less mature. Infants have the highest normal temperature, which decreases as people age. Some animals, especially small ones like [[rabbit]]s and [[cat]]s, also have a higher normal temperature than humans. Sometimes, high-grade fever can be a [[medical emergency]]. At or above 42&nbsp;°C (107.6&nbsp;F) organs start taking damage that may not be repairable. While most fevers are caused by [[Infection]], whether bacterial or viral, some fevers can be caused by cancers, including [[leukemia]],<ref>[http://www.leukemia-lymphoma.org/all_page?item_id=7026 Leukemia &nbsp;&#124;&nbsp;The Leukemia & Lymphoma Society]</ref> [[lymphoma]],<ref>{{Cite web |url=http://lymphoma.about.com/o