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Causes
By Mayo Clinic staffHypothermia occurs when your body loses heat faster than it produces it. The most common causes of hypothermia are exposure to cold weather conditions or cold water, but prolonged exposure to any environment colder than your body can lead to hypothermia if you aren't dressed appropriately or can't control the conditions. Specific conditions leading to hypothermia include:
- Wearing clothes that aren't warm enough for weather conditions
- Staying out in the cold too long
- Unable to get out of wet clothes or move to a warm, dry location
- Accidental falls in water, as in a boating accident
- Inadequate heating in the home, especially for older people and infants
- Air conditioning that is too cold, especially for older people and infants
How your body loses heat
The mechanisms of heat loss from your body include the following:
- Radiated heat. Most heat loss is due to heat radiated from unprotected surfaces of your body. Your head has a large surface area and accounts for about half of all heat loss.
- Direct contact. If you're in direct contact with something very cold, such as cold water or the cold ground, heat is conducted away from your body. Because water is very good at transferring heat from your body, body heat is lost much faster in cold water than in cold air. Water that is 65 F (18 C) — a relatively mild air temperature — can lead to hypothermia very quickly. Similarly, heat loss from your body is much faster if your clothes are wet, as when you're caught out in the rain.
- Wind. Wind removes body heat by carrying away the thin layer of warm air at the surface of your skin. A wind chill factor is important in causing heat loss. For example, if the outside temperature is 32 F (0 C) and the wind chill factor is minus 15 F (minus 26 C), your body loses heat as quickly as if the actual temperature outside were minus 15 F (minus 26 C).
- Hypothermia. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/print/sec21/ch319/ch319d.html. Accessed May 6, 2009.
- Ulrich AS, et al. Hypothermia and localized cold injuries. Emergency Medical Clinics of North America. 2004;22:281.
- McCullough L, et al. Diagnosis and treatment of hypothermia. American Family Physician. 2004;70:2325.
- Jurkovich GJ. Environmental cold-induced injury. Surgical Clinics of North America. 2007;87:247.
- Hypothermia: A cold weather hazard. National Institute on Aging. http://www.nia.nih.gov. Accessed May 4, 2009.
- Extreme cold: A prevention guide to promote your personal health and safety. Centers for Disease Control and Prevention. http://emergency.cdc.gov/disasters/winter/guide.asp. Accessed May 4, 2009.
- Winter safety tips. American Academy of Pediatrics. http://www.aap.org/advocacy/releases/decwintertips.cfm. Accessed May 4, 2009.
- Federal requirements and safety tips for recreational boats: Cold water survival. United States Coast Guard. http://www.uscgboating.org/safety/fedreqs/saf_cold.htm. Accessed May 8, 2009.
- Hypothermia and cold water. Canadian Red Cross. http://www.redcross.ca/article.asp?id=15204&tid=024. Accessed May 8, 2009.
