Extreme heat Hyperthermia is defined as an unusually high body temperature, often known as overheating– the opposite of hypothermia, which occurs when your body becomes extremely cold. When your body absorbs or produces more heat than it can dissipate, you have hyperthermia. The body’s average temperature is 98.6 degrees Fahrenheit. Any body temperature exceeding 99 or 100 degrees Fahrenheit is considered very warm.
Hyperthermia is usually caused by overexertion in hot, humid conditions. Most forms of hyperthermia may be avoided.