In children under age 17, a body temperature of 102 degrees Fahrenheit is considered dangerous, states Mayo Clinic. The danger point for adults is 103 F. The average body temperature is between 97 F and 99 F, depending on activity level and time of day.
A rise in body temperature causing fever may be caused by infection, certain medical conditions, or trauma such as stroke, heart attack, burns or heatstroke, reports WebMD. Heatstroke is a life-threatening condition requiring emergency medical attention.
An abnormally low body temperature, or hypothermia, is also dangerous, notes MedicineNet. Many doctors consider a core temperature below about 96 F as hypothermic. Hypothermia is usually caused by prolonged exposure to cold weather or immersion in cold water.