Hypothermia is a medical emergency that occurs when your body loses heat faster than it can produce heat, causing a dangerously low body temperature. Normal body temperature is around 98.6 F (37 C). Hypothermia (hi-poe-THUR-me-uh) occurs as your body temperature passes below 95 F (35 C).
When your body temperature drops, your heart, nervous system and other organs can't work normally. Left untreated, hypothermia can eventually lead to complete failure of your heart and respiratory system and to death.
Hypothermia is most often caused by exposure to cold weather or immersion in a cold body of water. Primary treatments for hypothermia are methods to warm the body back to a normal temperature.
Shivering is likely the first thing you'll notice as the temperature starts to drop because it's your body's automatic defense against cold temperature — an attempt to warm itself.
Signs and symptoms of mild hypothermia include:
As your body temperature drops, signs and symptoms of moderate to severe hypothermia include:
Someone with hypothermia usually isn't aware of his or her condition because the symptoms often begin gradually. Also, the confused thinking associated with hypothermia prevents self-awareness. The confused thinking can also lead to risk-taking behavior.
Typical signs of hypothermia in an infant include:
Hypothermia isn't always the result of exposure to extremely cold outdoor temperatures. An older person may develop mild hypothermia after prolonged exposure to indoor temperatures that would generally be fine for a younger or healthier adult. This can occur in a poorly heated home or in an air-conditioned home. Signs and symptoms of this type of hypothermia may not be as obvious.
Hypothermia 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:
The mechanisms of heat loss from your body include the following:
Older age. Older adults are more vulnerable to hypothermia for a number of reasons. The body's ability to regulate temperature and to sense cold may lessen with age.
Older people are also more likely to have a medical condition that affects temperature regulation. Some older adults may not be able to communicate when they are cold or may not be mobile enough to get to a warm location.
Very young age. Children lose heat faster than adults do. Children have a larger surface area-to-weight ratio than adults do, making them more prone to heat loss.
Children may also ignore the cold because they're having too much fun to think about it. And they may not have the judgment to dress properly in cold weather or to get out of the cold when they should. Infants may have a special problem with the cold because they have less efficient mechanisms for generating heat.
Hypothermia is a potentially dangerous drop in body temperature, usually caused by prolonged exposure to cold temperatures. The risk of cold exposure increases as the winter months arrive. But if you're exposed to cold temperatures on a spring hike or capsized on a summer sail, you can also be at risk of hypothermia.
Normal body temperature averages 98.6 degrees. With hypothermia, core temperature drops below 95 degrees. In severe hypothermia, core body temperature can drop to 82 degrees or lower.
Possible causes of hypothermia include:
Cold exposure. When the balance between the body's heat production and heat loss tips toward heat loss for a prolonged period, hypothermia can occur. Accidental hypothermia usually happens after cold temperature exposure without enough warm, dry clothing for protection. Mountain climbers on Mount Everest avoid hypothermia by wearing specialized, high-tech gear designed for that windy, icy environment.
However, much milder environments can also lead to hypothermia, depending on a person's age, body mass, body fat, overall health, and length of time exposed to cold temperatures. A frail, older adult in a 60-degree house after a power outage can develop mild hypothermia overnight. Infants and babies sleeping in cold bedrooms are also at risk.
During exposure to cold temperatures, most heat loss -- up to 90% -- escapes through your skin; the rest, you exhale from your lungs. Heat loss through the skin happens primarily through radiation and speeds up when skin is exposed to wind or moisture. If cold exposure is due to being immersed in cold water, heat loss can occur 25 times faster than it would if exposed to the same air temperature.
The hypothalamus, the brain's temperature-control center, works to raise body temperature by triggering processes that heat and cool the body. During cold temperature exposure, shivering is a protective response to produce heat through muscle activity. In another heat-preserving response -- called vasoconstriction -- blood vessels temporarily narrow.
Normally, the activity of the heart and liver produce most of your body heat. But as core body temperature cools, these organs produce less heat, in essence causing a protective "shut down" to preserve heat and protect the brain. Low body temperature can slow brain activity, breathing, and heart rate.
Confusion and fatigue can set in, hampering a person's ability to understand what's happening and make intelligent choices to get to safety.
People at increased risk for hypothermia include:
Hypothermia symptoms for adults include:
Hypothermia symptoms for infants include:
Recognizing the symptoms is the first step in diagnosing hypothermia. A specialized thermometer, available in most hospital emergency rooms, can detect very low core body temperatures and confirm a diagnosis.
Temperatures for mild, moderate, and severe hypothermia generally range from:
Mild hypothermia: 89-95 degrees Farenheit
Moderate hypothermia: 82-89 degrees Farenheit
Severe hypothermia: Lower than 82 degrees Farenheit
Because response to hypothermia varies among individuals, temperatures may differ.