MODEL RELEASED. Measuring oral temperature. Child clutching her forehead while holding a digital thermometer in her mouth. The metal bulb of the thermometer (not shown) is placed in the mouth, and the temperature is displayed in a window on the thermometer. A normal temperature is 36.3 degrees Celsius. Fever, also known as pyrexia, is defined as a temperature above 37 degrees Celsius, when measured orally. Most fevers are caused by bacterial or viral infections and may be accompanied by other symptoms such as shivering, sweating, thirst and hot skin.