When the temperature starts to drop, the body can start to shiver. Shivering is the body's attempt to warm itself. It is an automatic defense against cold temperature.

Symptoms of hypothermia include:

• Shivering.
• 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.
• In infants, bright red, cold skin.

People with hypothermia usually aren't aware of their condition. The symptoms often begin gradually. Also, the confused thinking associated with hypothermia prevents self-awareness. The confused thinking also can lead to risk-taking behavior.

When to see a doctor

Call 911 or your local emergency number if you suspect someone has hypothermia.

While waiting for emergency help to arrive, gently move the person inside if possible. Jarring movements can trigger dangerous irregular heartbeats. Carefully remove any wet clothing and replace it with warm, dry coats or blankets.

Hypothermia occurs when the 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 the body can lead to hypothermia if a person isn't dressed properly 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, such 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 the body include:

• Radiated heat. Most heat loss is due to heat radiated from unprotected surfaces of the body.
• Direct contact. Direct contact with something very cold takes heat away from the body. Examples include contact with cold water or the cold ground. Because water is very good at transferring heat from the body, body heat is lost much faster in cold water than in cold air. Similarly, heat loss from the body is much faster if clothes are wet, as from being caught out in the rain.
• Wind. Wind removes body heat by carrying away the thin layer of warm air at the surface of the skin. A wind chill factor is important in causing heat loss.

Risk factors for hypothermia include:

• Exhaustion. Fatigue reduces a person's ability to tolerate cold.
• 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 tell someone 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 also may ignore the cold because they're having too much fun to think about it. They may not have the judgment to dress properly in cold weather or to get out of the cold when they should.
• Mental conditions. People with a mental illness, dementia or other conditions that interfere with judgment may not dress properly 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 the body feel warm inside, but it causes blood vessels to expand. As a result, the surface of the skin loses heat more rapidly. Alcohol also reduces the body's natural shivering response.

  In addition, the use of alcohol or recreational drugs can affect judgment about the need to get inside or wear warm clothes in cold-weather conditions. A person who is intoxicated and passes out in cold weather is likely to develop hypothermia.

• Certain medical conditions. Some health disorders affect the body's ability to regulate body temperature. Examples include an underactive thyroid, also called hypothyroidism; poor nutrition or anorexia nervosa; diabetes; stroke; severe arthritis; Parkinson's disease; trauma; and spinal cord injuries.
• Medicines. Some drugs can change the body's ability to regulate its temperature. Examples include certain antidepressants, antipsychotics, narcotic pain medicines and sedatives.

People who develop hypothermia because of exposure to cold weather or cold water are also vulnerable to other cold-related injuries, including:

• Frostbite, which is when skin and underlying tissues become frozen.
• Gangrene, which is when body tissue decays and dies because blood flow is blocked.

Stay warm in cold weather

To stay warm in cold weather, remember the 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 cause a lot of sweat. The combination of wet clothing and cold weather can cause the body to lose 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.

Keep 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 often to warm themselves when they're playing outside.
• Don't let babies sleep in a cold room.

Winter car safety

When 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 the 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, a compass, and a bag of sand or kitty litter to spread for traction if the car gets 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.

Alcohol

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.

Cold-water safety

Water doesn't have to be extremely cold to cause hypothermia. Any water that's colder than usual body temperature causes heat loss. 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 uses up energy and may shorten survival time.
• Position the body to minimize heat loss. Use a body position known as the heat escape lessening posture (HELP) to reduce heat loss while you wait for help. Hold your knees to your chest to protect the trunk of the body. If your life jacket forces your face down into the water when in this position, straighten your legs and bring them tightly together, hold your arms to your sides, and tilt your head back.
• Huddle with others. If you've fallen into cold water with other people, keep warm by facing the others in a tight circle.
• Don't remove 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 people most at risk

Community outreach programs and social support services can be of great help for people most at risk of hypothermia. This includes infants, older adults, people who have mental or physical health conditions, and people who are homeless. If you are at risk or know someone at risk, contact your local public health office for available services, such as the following:

• Help with 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.

The diagnosis of hypothermia usually is clear based on a person's symptoms. The conditions in which the person with hypothermia became ill or was found also often make the diagnosis clear. Blood tests can help confirm hypothermia and its severity.

A diagnosis may not be clear, however, if the symptoms are mild. For example, hypothermia may not be considered when an older person who is indoors has symptoms of confusion, lack of coordination and speech problems.

Seek immediate medical attention for anyone who appears to have hypothermia. Until medical help is available, follow these first-aid guidelines for hypothermia.

First-aid tips

• Be gentle. When helping someone with hypothermia, handle them gently. Only move the person as much as is necessary. Don't massage or rub the person. Vigorous or jarring movements may trigger cardiac arrest.
• Move the person out of the cold. Move the person to a warm, dry location if possible. If moving is not possible, shield the person from the cold and wind as much as possible. The person should be kept in a flat position if possible.
• Remove wet clothing. If the person is wearing wet clothing, remove it. Cut away clothing if necessary to avoid too much movement.
• Cover the person with blankets. Use layers of dry blankets or coats to warm the person. Cover the person's head, leaving only the face exposed.
• Insulate the person's body from the cold ground. If you're outside, lay the person flat on a blanket or other warm surface.
• Monitor breathing. A person with severe hypothermia may appear unconscious, with no clear signs of a pulse or breathing. If the person's breathing has stopped or appears dangerously low or shallow, begin CPR right away if you're trained.
• Supply warm beverages. If the affected person is alert and able to swallow, give the person a warm, sweet, nonalcoholic, noncaffeinated drink. Warm drinks can help warm the body.

• Use warm, dry compresses. Use first-aid warm compresses, which are plastic fluid-filled bags that warm up when squeezed. Other options include a makeshift compress of warm water in a plastic bottle or a dryer-warmed towel.

Apply the compresses only to the neck, chest wall or groin. Don't apply them to the arms or legs. Heat applied to the arms and legs forces cold blood back toward the heart, lungs and brain, causing the core body temperature to drop. This can be fatal.

• Don't apply direct heat. Don't use hot water, a heating pad or a heating lamp to warm the person. The extreme heat can damage the skin. It also can trigger irregular heartbeats that cause the heart to stop.

Medical treatment

Depending on the severity of hypothermia, emergency medical care for hypothermia may include one of the following interventions to raise the body temperature:

• Passive rewarming. For mild hypothermia, covering the person with heated blankets and offering them warm fluids to drink may be enough.
• Blood rewarming. Blood may be drawn, warmed and recirculated in the body. A common method of warming blood is the use of a hemodialysis machine, which is usually used to filter blood in people with poor kidney function. Heart bypass machines also may need to be used.
• Warm intravenous fluids. A warmed solution of salt water may be put into a vein to help warm the blood.
• Airway rewarming. The use of humidified oxygen, given through a mask or nasal tube, can warm the airways and help raise the temperature of the body.
• Irrigation. A warm saltwater solution may be used to warm certain areas of the body, such as the area around the lungs or the abdominal cavity. The warm liquid is delivered to the affected area through small tubes called catheters.