Hypothermia is the lowering of the body's core temperature. There are two types of hypothermia, acute and chronic. Acute hypothermia is the rapid lowering of the body's core temp.
Chronic hypothermia is the slow lowering of the body's core temp.
If the temperature drop occurs in less than 4 hours it is acute, otherwise it is chronic. Acute hypothermia is also called immersion hypothermia and typically occurs when a person is in cold water. It is important to note the difference between the two since treatment will be different. Hypothermia is considered severe when the body's core temperature drops below 90 degrees F and mild from normal body temperature to 90 degrees F. A difference between acute and chronic hypothermia is the severity of something called afterdrop. This is the continued dropping of the body's core temperature after the person has been brought to a warm place.