What is hypothermia?

Hypothermia occurs when body temperature drops below 95°F (35°C). It's a medical emergency. Normal body temperature is about 98.6°F (37°C). Hypothermia happens most often in very cold temperatures. But even cool temperatures (above 40°F or 4°C) can be dangerous to a person who is chilled from rain, sweat, or being in cold water for a long time.

Hypothermia can progress from mild, to moderate, to severe. As the body temperature drops, it affects body organs, such as the brain. This makes it hard to think clearly or move well. It can also affect the heart. This causes abnormal heart rate and rhythm. Dropping body temperature affects the ability to breathe normally and causes loss of other body functions. If not treated, hypothermia can lead to death.

What causes hypothermia?

Hypothermia occurs when you lose more body heat than your body can make. It can be brought on by staying in cold temperatures for a long time.

Who is at risk for hypothermia?

The following people are most at risk for hypothermia:

Older adults, as they often have other illnesses, such as hypothyroidism, heart disease, or circulation problems. Or they may take medicines that interfere with the body's ability to regulate its temperature.
Older adults without correct food, clothing, or heat. Often they may sit alone for hours or days at a time in a cold apartment or home. Poor nutrition also makes them more at risk from the cold.
Babies and toddlers sleeping in cold bedrooms
People who stay outdoors for long periods of time, such as the homeless, hikers, and hunters
People who are intoxicated with alcohol or other substances and "pass out" in a cold environment

Even young, healthy adults are affected by hypothermia when exposed to the cold for long periods of time.

What are the symptoms of hypothermia?

These are the most common symptoms of hypothermia:

Shivering, but conscious
Cold skin
Drowsiness
Confusion without shivering
Slow, slurred speech, or shallow breathing
Movements that may be slow and uncoordinated
As hypothermia gets worse, stiffness in the arms and legs
Slow heartbeat, weak pulse or low blood pressure
Slowed breathing rate
Loss of consciousness
In infants, cold and bright red skin, or very low energy

Untreated, hypothermia can be fatal. If the person has symptoms of hypothermia even if a temperature can’t be taken, call 911.

How is hypothermia diagnosed?

If someone has hypothermia symptoms, a healthcare provider will do a physical exam. The provider will find out about the person’s exposure to the cold. They will also check their level of consciousness and vital signs. The provider will want to know if the person has a health condition that puts them at risk for hypothermia. And the provider will check for a body (core) temperature of less than 95° F (35° C).

Other tests that may be done are blood tests, a chest X-ray, and an ECG (electrocardiogram).

Body temperature can vary depending on many factors. These include where the temperature is taken on the body, and the type of thermometer used. A low-reading thermometer is needed for an accurate temperature. Standard thermometers are not able to measure temperatures below 94° F (about 34° C). A healthcare provider uses thermometers that can more accurately measure the core body temperature. These thermometers are often inserted into the rectum to get an accurate core temperature.

How is hypothermia treated?

The goal of treatment is to prevent further heat loss and rewarm your body. People with hypothermia need medical care right away. While waiting for medical care, try these warming methods to help the person:

Be careful to not handle the person roughly. Rough movements can trigger dangerous heart rhythms.
Gently get the person into a warm room or shelter.
Carefully remove any wet clothing immediately.
Warm the center of the body first—the chest, neck, head, and groin—using an electric blanket, if it is available. Or use skin-to-skin contact, with your own body heat providing warmth to the person.
Encourage sips of warm drinks, which can be helpful. But never give a person with hypothermia any alcohol. And never try to give an unconscious person something to drink.
Once the person’s body temperature begins to increase, keep them dry and wrapped in warm blankets.

Hospital treatment depends on the degree of hypothermia. Rewarming methods of treatment may include:

Removing wet clothing
Using warm blankets or a commercial forced-air body warming blanket
Giving warm liquids to drink if the person is awake during treatment
Giving warmed oxygen through a mask and nasal tube
Giving heated fluids through an IV (intravenous) line or other methods. This helps raise body temperature quickly.

Some other methods to rewarm the body can include hemodialysis (blood is pumped through a tube into the machine to filter and warmed and returned back into the body) or use of a heart-lung machine (pumps blood out of the body and is rewarmed and oxygen is added and returned back to the body).

Depending on how severe the hypothermia is, other treatments can include:

A breathing tube inserted into the windpipe (mechanical ventilation)
Treatment of abnormal heart rhythms
CPR

What are possible complications of hypothermia?

Hypothermia and frostbite both occur when skin is exposed to cold and the body temperature falls.

With frostbite, the body tissues become frozen. Long-lasting (permanent) damage may happen if the affected area is not treated right away. In most cases, the person is not aware of frostbite because the frozen skin and tissue are numb. In severe cases, gangrene can occur. This is when the affected area’s skin turns black, and tissue dies. In the most severe cases, a body part may need to be amputated. In most cases, affected body parts include the nose, ears, fingers, toes, cheeks, and chin.

Severe hypothermia can cause an irregular heartbeat leading to heart failure and death.

Can hypothermia be prevented?

Hypothermia can be prevented by taking these steps to keep warm in the cold:

Always check the weather before you go out. Be prepared in case you get stranded in cold weather. Keep first aid kits, packaged and canned food, and dry blankets and clothing in your car. When swimming or boating, have these same emergency supplies. Also have rescue items, such as life jackets, on hand.
Eat enough food each day. When you’re cold, your body uses up more calories. Also, you need to have some body fat for your body to stay warm.
Limit the amount of caffeine or alcohol you drink when it’s cold. These cause your blood vessels to widen, which can lower your body temperature. Alcohol can also affect your ability to tell if you are getting too cold.
Check with your healthcare provider to see if certain health problems you have or medicines you take can affect your body temperature. You may need to take extra steps to protect yourself from hypothermia.
Always do outdoor cold-weather sports or activities with another person. Wear multiple layers. If clothing gets wet, go indoors and remove wet items as soon as possible. And be sure to get enough food and rest to help your body be ready to protect itself against cold.
For older adults, keep a warm environment. Keep your home’s temperature at 68 degrees or above. There may be winterization programs and fuel assistance programs available to help with costs of heating the home. Wear a hat, since lots of heat is lost from the head. Protect fingers and toes, which are at risk from the cold. Having warm food and drinks can help and prevent dehydration.
Dress infants and young children for the temperature. Don't take infants and children out in cold weather without the correct hats, coats, pants, and gloves. Pay close attention to toddlers who may get wet in the snow and not realize how cold they are becoming. Make sure they change out of their wet clothing as soon as possible.

When should I call 911?

Call 911 if you have:

Body temperature below 95°F (35°C)
Skin that is cold, numb, or tingly
Skin that is blue, white, gray, or waxy
Return of symptoms, such as confusion, memory loss, slurred speech, and slow and uncoordinated body movements
Heartbeat changes
Chest pain or trouble breathing
Loss of consciousness

Key points about hypothermia

Hypothermia occurs when body temperature drops below 95°F (35°C). It's a medical emergency.
It happens most often in very cold temperatures. But even cool temperatures can be dangerous if someone is chilled from rain, sweat, or being in cold water for a long time.
As the body temperature drops, it affects body organs, such as the brain and the heart.
The goal of treatment is to prevent further heat loss and rewarm the body.
If not treated, hypothermia can lead to death.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

Know the reason for your visit and what you want to happen.
Before your visit, write down questions you want answered.
Bring someone with you to help you ask questions and remember what your provider tells you.
At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.
Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
Ask if your condition can be treated in other ways.
Know why a test or procedure is recommended and what the results could mean.
Know what to expect if you do not take the medicine or have the test or procedure.
If you have a follow-up appointment, write down the date, time, and purpose for that visit.
Know how you can contact your healthcare provider if you have questions.