Hyperthermia occurs when the body's temperature becomes unusually high, often due to heat exposure, intense physical activity, or certain illnesses. This condition can create a dangerous cycle where elevated body temperature increases the metabolic rate, generating more heat and potentially leading to organ failure and brain damage. A severe form of hyperthermia, called heat stroke, can raise body temperature to life-threatening levels. Fever, on the other hand, is a controlled form of hyperthermia triggered by infections, allergies, or cancer. In this case, immune cells release cytokines to elevate body temperature as part of the body's defense mechanism.

Conversely, hypothermia occurs when the body temperature falls abnormally low, typically due to prolonged exposure to cold. This condition slows respiratory and heart rates, reduces metabolic activity, and, in extreme cases, can lead to coma, cardiac arrest, or death.

Preventing and treating hyperthermia and hypothermia involves strategies such as maintaining proper hydration, avoiding excessive heat or cold exposure, and using cooling or warming techniques as needed.