Any temperature over the normal body temperature of 98.6 degrees Fahrenheit is considered to be a fever, according to WebMD. However, in medicine any temperature over 100.4 F is considered to be a fever.
Body temperature is a measurement of a person's ability to generate heat, according to WebMD. The human body is good at keeping body temperature steady and has many mechanisms to cool down or heat up the body's internal temperature when necessary. When people are too hot, blood vessels underneath their skin dilate to carry excess heat to the skin's surface. When too cold, the same blood vessels contract to conserve heat.