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 falls 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 eventually to death.
Hypothermia is often caused by exposure to cold weather or immersion in cold 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 hypothermia include:
- Slurred speech or mumbling
- Slow, shallow breathing
- Weak pulse
- Clumsiness or lack of coordination
- Drowsiness or very low energy
- Confusion or memory loss
- Loss of consciousness
- Bright red, cold skin (in infants)
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.
When to see a doctor
Call 911 or your local emergency number if you suspect someone has hypothermia.
While you wait for emergency help to arrive, gently move the person inside if possible. Jarring movements can trigger dangerous irregular heartbeats. Carefully remove his or her wet clothing, replacing it with warm, dry coats or blankets.
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:
- Wearing clothes that aren't warm enough for weather conditions
- Staying out in the cold too long
- Being unable to get out of wet clothes or move to a warm, dry location
- Falling into the water, as in a boating accident
- Living in a house that's too cold, either from poor heating or too much air conditioning
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.
- 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. 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.
Risk factors for hypothermia include:
- Exhaustion. Your tolerance for cold diminishes when you are fatigued.
- Older age. The body's ability to regulate temperature and to sense cold may lessen with age. And some older adults may not be able to communicate when they are cold or to move to a warm location if they do feel cold.
- Very young age. Children lose heat faster than adults do. 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.
- Mental problems. People with a mental illness, dementia or other conditions that interfere with judgment may not dress appropriately for the weather or understand the risk of cold weather. People with dementia may wander from home or get lost easily, making them more likely to be stranded outside in cold or wet weather.
- Alcohol and drug use. Alcohol may make your body feel warm inside, but it causes your blood vessels to expand, resulting in more rapid heat loss from the surface of your skin. The body's natural shivering response is diminished in people who've been drinking alcohol. In addition, the use of alcohol or recreational drugs can affect your judgment about the need to get inside or wear warm clothes in cold weather conditions. If a person is intoxicated and passes out in cold weather, he or she is likely to develop hypothermia.
- Certain medical conditions. Some health disorders affect your body's ability to regulate body temperature. Examples include an underactive thyroid (hypothyroidism), poor nutrition or anorexia nervosa, diabetes, stroke, severe arthritis, Parkinson's disease, trauma, and spinal cord injuries.
- Medications. Some drugs can change the body's ability to regulate its temperature. Examples include certain antidepressants, antipsychotics, narcotic pain medications and sedatives.
Mayo Clinic Minute: Why the risk of frostbite is greater than you think
As winter drags on and temperatures drop way down, your risk of cold-related injury like frostbite can go way up.
"Literally think of it as freezing of the tissues," Dr. Sanj Kakar Mayo Clinic Orthopedic hand and wrist surgeon says frostbite is more common than many people think.
"We tend to see frostbite, for example, when the temperature is 5 degrees Fahrenheit with minimal windchill," Dr. Kakar explains.
If the windchill drops below negative 15 degrees Fahrenheit, not unheard of in the northern half of the U.S., frostbite can set in within half an hour.
The most vulnerable areas of frostbite are your nose, ears, fingers and toes.
"Initially [with] the milder forms, you can get some pain and some numbness of the tips, but the skin can change its color," Dr. Kakar says. "It can be red. It can be white. Or it can be blue. And you can get these blisters on your hands. And it can be a very serious injury."
The worst cases, the tissue can die, and you may need surgery to remove it.
So who's most at risk?
"[Those most at risk are] certain patients with diabetes, patients who have previous history of frostbite are prone to it, the elderly or your very young children, and also, for example, if you're dehydrated," he says.
People who develop hypothermia because of exposure to cold weather or cold water are also vulnerable to other cold-related injuries, including:
- Freezing of body tissues (frostbite)
- Decay and death of tissue resulting from an interruption in blood flow (gangrene)
Staying warm in cold weather
Before you or your children step out into cold air, remember the advice that follows with the simple acronym COLD — cover, overexertion, layers, dry:
- Cover. Wear a hat or other protective covering to prevent body heat from escaping from your head, face and neck. Cover your hands with mittens instead of gloves.
- Overexertion. Avoid activities that would cause you to sweat a lot. The combination of wet clothing and cold weather can cause you to lose body heat more quickly.
- Layers. Wear loosefitting, layered, lightweight clothing. Outer clothing made of tightly woven, water-repellent material is best for wind protection. Wool, silk or polypropylene inner layers hold body heat better than cotton does.
- Dry. Stay as dry as possible. Get out of wet clothing as soon as possible. Be especially careful to keep your hands and feet dry, as it's easy for snow to get into mittens and boots.
Keeping children safe from the cold
To help prevent hypothermia when children are outside in the winter:
- Dress infants and young children in one more layer than an adult would wear in the same conditions.
- Bring children indoors if they start shivering — that's the first sign that hypothermia is starting.
- Have children come inside frequently to warm themselves when they're playing outside.
- Don't let babies sleep in a cold room.
Winter car safety
Whenever you're traveling during bad weather, be sure someone knows where you're headed and at what time you're expected to arrive. That way, if you get into trouble on your way, emergency responders will know where to look for your car.
It's also a good idea to keep emergency supplies in your car in case you get stranded. Supplies may include several blankets, matches, candles, a clean can where you can melt snow into drinking water, a first-aid kit, dry or canned food, a can opener, tow rope, booster cables, compass, and a bag of sand or kitty litter to spread for traction if you're stuck in the snow. If possible, travel with a cellphone.
If you're stranded, put everything you need in the car with you, huddle together and stay covered. Run the car for 10 minutes each hour to warm it up. Make sure a window is slightly open and the exhaust pipe isn't covered with snow while the engine is running.
To avoid alcohol-related risks of hypothermia, don't drink alcohol:
- If you're going to be outside in cold weather
- If you're boating
- Before going to bed on cold nights
Water doesn't have to be extremely cold to cause hypothermia. Any water that's colder than normal body temperature causes heat loss. (8, p2) The following tips may increase your survival time in cold water if you accidentally fall in:
- Wear a life jacket. If you plan to ride in a watercraft, wear a life jacket. A life jacket can help you stay alive longer in cold water by enabling you to float without using energy and by providing some insulation. Keep a whistle attached to your life jacket to signal for help.
- Get out of the water if possible. Get out of the water as much as possible, such as climbing onto a capsized boat or grabbing onto a floating object.
- Don't attempt to swim unless you're close to safety. Unless a boat, another person or a life jacket is close by, stay put. Swimming will use up energy and may shorten survival time.
- Position your body to minimize heat loss. Use a body position known as the heat escape lessening position (HELP) to reduce heat loss while you wait for assistance. Hold your knees to your chest to protect the trunk of your body. If you're wearing a life jacket that turns your face down in this position, bring your legs tightly together, your arms to your sides and your head back.
- Huddle with others. If you've fallen into cold water with other people, keep warm by facing each other in a tight circle.
- Don't remove your clothing. While you're in the water, don't remove clothing because it helps to insulate you from the water. Buckle, button and zip up your clothes. Cover your head if possible. Remove clothing only after you're safely out of the water and can take measures to get dry and warm.
Help for at-risk people
For people most at risk of hypothermia — infants, older adults, people who have mental or physical problems, and people who are homeless — community outreach programs and social support services can be of great help. If you're at risk or know someone at risk, contact your local public health office for available services, such as the following:
- Assistance for paying heating bills
- Check-in services to see if you and your home are warm enough during cold weather
- Homeless shelters
- Community warming centers, safe and warm daytime locations where you can go during cold weather