Hyperthermia is a high body temperature. It happens when a person is not able to control their body temperature. This can happen for many reasons, like very hot weather, fever, and some medicines or illegal drugs.

Doctors define hyperthermia as a body temperature that is over 101 degrees Fahrenheit (equal to 38.3 degrees Celsius). This is higher than the average human body temperature, which is normally around 98.6 degrees Fahrenheit (37 degrees Celsius). When a person gets hyperthermia, they can have heat-related injuries, where the high body temperature hurts the body.