Hypothermia happens when a person’s core body temperature is lower than 35°C (95°F). Hypothermia has three levels: acute, subacute, or chronic. Acute hypothermia is caused by a rapid loss of body heat, usually from immersion in cold water.
Subacute hypothermia often happens in cool outdoor weather (below 10°C or 50°F) when wind chill, wet or too little clothing, fatigue, and/or poor nutrition lower the body’s ability to cope with cold. Chronic hypothermia happens from ongoing exposure to cold indoor temperatures (below 16°C or 60°F). The poor, the elderly, people who have hypothyroidism, people who take sedative-hypnotics, and drug and alcohol abusers are prone to chronic hypothermia, and they typically: