Hypothermia occurs when more heat escapes from your body than your body can produce. Signs and symptoms of hypothermia may include gradual loss of mental and physical abilities. Severe hypothermia can lead to death.
For most people, hypothermia isn't a serious risk. Still, each year nearly 700 people in the United States die of hypothermia. Prolonged exposure to cold air or cold water temperatures are common causes.
When you're outdoors enjoying such activities as camping, hunting, fishing, boating and skiing, be aware of weather conditions and whether you or others with you are wet and cold. If you get cold and wet, move indoors and get warm and dry early — before you develop hypothermia.
Signs and symptoms
Hypothermia usually occurs gradually. Often, people aren't aware that they need help, much less medical attention.
Common signs to look for are shivering, which is your body's attempt to generate heat through muscle activity, and the "-umbles":
Stumbles
Mumbles
Fumbles
Grumbles
These behaviors may be a result of changes in consciousness and motor coordination caused by hypothermia. Other hypothermia symptoms may include:
Slurred speech
Abnormally slow rate of breathing
Cold, pale skin
Fatigue, lethargy or apathy
The severity of hypothermia can vary, depending on how low your core body temperature goes. Severe hypothermia eventually leads to cardiac and respiratory failure, then death.
Causes
Unlike other warm-blooded animals that have a layer of fur or blubber to keep them warm, you need an extra layer of clothing to keep you warm when it's cold outside. Without that extra layer of clothing, more heat escapes from your body than your body can produce. If too much heat escapes, the result is hypothermia. Exposure to cold water and certain medical conditions also can cause hypothermia.
Your normal core body temperature is usually right around 98.6 F. In hypothermia, your body fails to maintain a normal temperature. An internal body temperature of 95 F or lower signals hypothermia.
The cause of hypothermia usually is extended exposure to cold temperatures or a cool, damp environment. Other contributing causes include inadequate clothing and neglecting to adequately cover your extremities, particularly your head — a disproportionate amount of heat is lost through your head.
Hypothermia in milder weather
Hypothermia can happen not just in cold winter weather, when there are low temperatures or low wind chill factors, but under milder conditions as well. A rain shower that soaks you to the skin on a cool day can lead to hypothermia if you don't move inside to warm up and dry off. If you stay outside, evaporation of the water from your skin further cools your body, lowering your internal temperature. A wind blowing over the wet parts of your body greatly increases evaporation and cooling.
An accidental fall into cold water is especially likely to lead to hypothermia. Hypothermia may develop within minutes of being exposed to cold water, or it may take several hours, depending on the water temperature. Water doesn't have to be icy cold to cause hypothermia. Your body loses heat more quickly in water than in air. Any water temperature lower than your body temperature causes your body to lose at least some heat.
Risk factors
Being in extreme cold, wearing wet clothes — especially in the presence of wind — and being in cold water can all play a part in increasing your chances of hypothermia. In addition, other factors make you more vulnerable:
Advanced age. People age 65 and older are especially vulnerable because they may have other illnesses or take medications that can interfere with the body's ability to regulate temperature.
Very young age. Children usually lose heat faster than adults do. Children have a larger head-to-body ratio than adults do, making them more prone to heat loss through the head. 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 feel cold. Infants may have a special problem with the cold because they have less efficient mechanisms for generating heat.
Mental impairment. People with Alzheimer's disease or another illness that causes mental impairment may not be aware of the risks of being out in the cold. Wandering is not uncommon among people with Alzheimer's, and some affected people may stray away from home and be unable to find their way back on their own. Being stranded leaves them vulnerable to the weather.
Alcohol and drug use. Alcohol may make your body feel warm inside, but it lowers your body's ability to retain heat. Both alcohol and drugs such as marijuana can keep your blood vessels dilated, restrict your shivering response, impair your judgment and alter your awareness of weather conditions.
Certain medical conditions. Some health disorders affect your body's ability to respond to cold or to produce heat. Examples include untreated underactive thyroid (hypothyroidism), stroke, severe arthritis, Parkinson's disease, trauma, spinal cord injuries, burns, blood vessel or nerve disorders that affect sensation in your extremities (for example, peripheral neuropathy in people with diabetes), dehydration and any condition that limits activity or restrains the normal flow of blood. Older adults are more likely to have one or more of these risk factors.
Water conditions. Factors contributing to your risk of hypothermia in cold water include the temperature of the water and the length of time you spend in it. Rescue time is crucial when a person accidentally falls into cold water. Chances of survival are affected by how cold the water is: The colder the water, the less the chance of survival.
Water temperature Time until exhaustion or unconsciousness Expected time of survival in the water
Under 32 F (icy waters) Less than 15 minutes Less than 15 to 45 minutes
32.5 to 40 F (Lake Superior in spring) 15 to 30 minutes 30 to 90 minutes
40 to 50 F (Maine coastal waters in spring) 30 to 60 minutes 1 to 3 hours
50 to 60 F (Central Pacific coastal waters year-round) 1 to 2 hours 1 to 6 hours
60 to 70 F (Gulf of Mexico in winter) 2 to 7 hours 2 to 40 hours
70 to 80 F (Gulf of Mexico in spring and fall) 3 to 12 hours 3 hours to indefinite
More than 80 F (Key West coastal waters in summer) Indefinite Indefinite
Source: United States Search and Rescue Task Force
When to seek medical advice
The signs and symptoms of the person suffering from exposure to the cold are the strongest indicators of hypothermia. Seek immediate medical care for any person who has been exposed to cold air or water and who is shivering, appears disoriented, shows a lack of coordination, has cold and pale skin, appears tired, and is slurring speech. Try to keep the person warm and dry, preferably indoors or at least out of the wind, until help arrives.
Complications
Complications depend on how low your body temperature falls. If you're in water, you may lose consciousness and drown before your temperature drops low enough to cause death by hypothermia. Other complications of hypothermia may include:
Frostbite
Loss of limbs
Coma
The lower your core body temperature, the greater your chance of complications and permanent damage.
Treatment
Seek immediate medical attention for anyone who appears to have hypothermia. Until medical help is available, follow these hypothermia treatment guidelines for caring for someone who is affected.
What to do
Move the person out of the cold. Preventing additional heat loss is crucial. If you're unable to move the person out of the cold, shield the person from the cold and wind as best you can.
Remove wet clothing. If the person is wearing wet clothing, remove it and replace it with a dry covering. Cover the person's head. Try not to move the person too much. Cut away clothing if you need to.
Insulate the person's body from the cold ground. Lay the person faceup on a blanket or other warm surface.
Monitor breathing. A person with severe hypothermia may appear unconscious, with no apparent signs of a pulse or breathing. If the person's breathing has stopped or appears dangerously low or shallow, begin cardiopulmonary resuscitation (CPR) immediately if you're trained.
Share body heat. To warm the person's body, remove your clothing and lie next to the person, making skin-to-skin contact. Then cover both of your bodies with a blanket.
Provide warm beverages. If the affected person is alert and is able to swallow, have the person drink a warm, nonalcoholic beverage to help warm the body.
What not to do
Don't apply direct heat. Don't use hot water, a heating pad or a heating lamp to warm the person. Instead, apply warm compresses to the neck, chest wall and groin. Don't attempt to warm the arms and 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 massage or rub the person. Handle people with hypothermia gently because they're at risk of cardiac arrest.
Don't provide alcoholic beverages. Alcohol lowers the body's ability to retain heat.
What a doctor may do
A doctor will be able to take steps to warm the body from the inside out, if necessary. One method may involve giving the person warm fluids intravenously.
In severe cases of hypothermia, a process called hemodialysis may restore normal body temperatures quickly. Hemodialysis is a medical procedure that removes extra fluid, chemicals and wastes from the blood by filtering the blood through an artificial kidney. It's often used in people with kidney failure. In a hypothermia situation, the blood is removed purely to warm it rapidly outside the body and then have it returned to the body.
Prevention
For people most at risk of hypothermia — people who are older, who have mental or physical impairments, or who are homeless — community outreach programs and medical and social support services can be of great help. Identifying and checking in on vulnerable people and groups, avoiding prolonged exposure to the cold, and ensuring adequate heating are good steps to take toward hypothermia prevention. Monitoring bracelets may provide assistance for people who have a tendency to wander from home.
Avoid excessive alcohol consumption and the use of illegal substances, because these may increase your risk of hypothermia. Also, don't drink alcohol and operate a boat or other watercraft. Alcohol can impair your ability to navigate the waters, increasing your risk of an accident and of falling into cold water.
Staying healthy 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. Mittens are more effective than gloves are because mittens keep your fingers in closer contact with one another.
Overexertion. Avoid activities that would cause you to sweat a lot. The combination of wet clothing and cold weather can give you chills.
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 more body heat than cotton does.
Dry. Stay as dry as possible. In the winter, pay special attention to places where snow can enter, such as in loose mittens or snow boots.
During cold-weather months, keep emergency supplies in your car in case you get stranded. Supplies may include several blankets, matches, candles and some foodstuffs, such as granola bars or crackers. A cell phone also can come in handy. If your car is stuck in a snowbank, be careful about leaving the engine running, because infiltration of carbon monoxide inside the car may pose a silent danger.
Cold-water cautions
Water doesn't have to be extremely cold to cause hypothermia. Any water that's colder than body temperature causes heat loss. Water that's colder than 70 F can quickly begin to cause hypothermia. 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 allowing you to float without using energy and providing some insulation.
Don't panic. If you're unable to swim to safety, stay calm. Unnecessary movements require you to exert extra energy and lose body heat.
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. Buckle, button and zip up your clothes. Cover your head if you have a hood. The layer of water between your clothing and your body will be warmed and help insulate you.
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 expends extra energy, lowers body temperature and can shorten survival time.
By Mayo Clinic Staff
Jun 8, 2007
For most people, hypothermia isn't a serious risk. Still, each year nearly 700 people in the United States die of hypothermia. Prolonged exposure to cold air or cold water temperatures are common causes.
When you're outdoors enjoying such activities as camping, hunting, fishing, boating and skiing, be aware of weather conditions and whether you or others with you are wet and cold. If you get cold and wet, move indoors and get warm and dry early — before you develop hypothermia.
Signs and symptoms
Hypothermia usually occurs gradually. Often, people aren't aware that they need help, much less medical attention.
Common signs to look for are shivering, which is your body's attempt to generate heat through muscle activity, and the "-umbles":
Stumbles
Mumbles
Fumbles
Grumbles
These behaviors may be a result of changes in consciousness and motor coordination caused by hypothermia. Other hypothermia symptoms may include:
Slurred speech
Abnormally slow rate of breathing
Cold, pale skin
Fatigue, lethargy or apathy
The severity of hypothermia can vary, depending on how low your core body temperature goes. Severe hypothermia eventually leads to cardiac and respiratory failure, then death.
Causes
Unlike other warm-blooded animals that have a layer of fur or blubber to keep them warm, you need an extra layer of clothing to keep you warm when it's cold outside. Without that extra layer of clothing, more heat escapes from your body than your body can produce. If too much heat escapes, the result is hypothermia. Exposure to cold water and certain medical conditions also can cause hypothermia.
Your normal core body temperature is usually right around 98.6 F. In hypothermia, your body fails to maintain a normal temperature. An internal body temperature of 95 F or lower signals hypothermia.
The cause of hypothermia usually is extended exposure to cold temperatures or a cool, damp environment. Other contributing causes include inadequate clothing and neglecting to adequately cover your extremities, particularly your head — a disproportionate amount of heat is lost through your head.
Hypothermia in milder weather
Hypothermia can happen not just in cold winter weather, when there are low temperatures or low wind chill factors, but under milder conditions as well. A rain shower that soaks you to the skin on a cool day can lead to hypothermia if you don't move inside to warm up and dry off. If you stay outside, evaporation of the water from your skin further cools your body, lowering your internal temperature. A wind blowing over the wet parts of your body greatly increases evaporation and cooling.
An accidental fall into cold water is especially likely to lead to hypothermia. Hypothermia may develop within minutes of being exposed to cold water, or it may take several hours, depending on the water temperature. Water doesn't have to be icy cold to cause hypothermia. Your body loses heat more quickly in water than in air. Any water temperature lower than your body temperature causes your body to lose at least some heat.
Risk factors
Being in extreme cold, wearing wet clothes — especially in the presence of wind — and being in cold water can all play a part in increasing your chances of hypothermia. In addition, other factors make you more vulnerable:
Advanced age. People age 65 and older are especially vulnerable because they may have other illnesses or take medications that can interfere with the body's ability to regulate temperature.
Very young age. Children usually lose heat faster than adults do. Children have a larger head-to-body ratio than adults do, making them more prone to heat loss through the head. 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 feel cold. Infants may have a special problem with the cold because they have less efficient mechanisms for generating heat.
Mental impairment. People with Alzheimer's disease or another illness that causes mental impairment may not be aware of the risks of being out in the cold. Wandering is not uncommon among people with Alzheimer's, and some affected people may stray away from home and be unable to find their way back on their own. Being stranded leaves them vulnerable to the weather.
Alcohol and drug use. Alcohol may make your body feel warm inside, but it lowers your body's ability to retain heat. Both alcohol and drugs such as marijuana can keep your blood vessels dilated, restrict your shivering response, impair your judgment and alter your awareness of weather conditions.
Certain medical conditions. Some health disorders affect your body's ability to respond to cold or to produce heat. Examples include untreated underactive thyroid (hypothyroidism), stroke, severe arthritis, Parkinson's disease, trauma, spinal cord injuries, burns, blood vessel or nerve disorders that affect sensation in your extremities (for example, peripheral neuropathy in people with diabetes), dehydration and any condition that limits activity or restrains the normal flow of blood. Older adults are more likely to have one or more of these risk factors.
Water conditions. Factors contributing to your risk of hypothermia in cold water include the temperature of the water and the length of time you spend in it. Rescue time is crucial when a person accidentally falls into cold water. Chances of survival are affected by how cold the water is: The colder the water, the less the chance of survival.
Water temperature Time until exhaustion or unconsciousness Expected time of survival in the water
Under 32 F (icy waters) Less than 15 minutes Less than 15 to 45 minutes
32.5 to 40 F (Lake Superior in spring) 15 to 30 minutes 30 to 90 minutes
40 to 50 F (Maine coastal waters in spring) 30 to 60 minutes 1 to 3 hours
50 to 60 F (Central Pacific coastal waters year-round) 1 to 2 hours 1 to 6 hours
60 to 70 F (Gulf of Mexico in winter) 2 to 7 hours 2 to 40 hours
70 to 80 F (Gulf of Mexico in spring and fall) 3 to 12 hours 3 hours to indefinite
More than 80 F (Key West coastal waters in summer) Indefinite Indefinite
Source: United States Search and Rescue Task Force
When to seek medical advice
The signs and symptoms of the person suffering from exposure to the cold are the strongest indicators of hypothermia. Seek immediate medical care for any person who has been exposed to cold air or water and who is shivering, appears disoriented, shows a lack of coordination, has cold and pale skin, appears tired, and is slurring speech. Try to keep the person warm and dry, preferably indoors or at least out of the wind, until help arrives.
Complications
Complications depend on how low your body temperature falls. If you're in water, you may lose consciousness and drown before your temperature drops low enough to cause death by hypothermia. Other complications of hypothermia may include:
Frostbite
Loss of limbs
Coma
The lower your core body temperature, the greater your chance of complications and permanent damage.
Treatment
Seek immediate medical attention for anyone who appears to have hypothermia. Until medical help is available, follow these hypothermia treatment guidelines for caring for someone who is affected.
What to do
Move the person out of the cold. Preventing additional heat loss is crucial. If you're unable to move the person out of the cold, shield the person from the cold and wind as best you can.
Remove wet clothing. If the person is wearing wet clothing, remove it and replace it with a dry covering. Cover the person's head. Try not to move the person too much. Cut away clothing if you need to.
Insulate the person's body from the cold ground. Lay the person faceup on a blanket or other warm surface.
Monitor breathing. A person with severe hypothermia may appear unconscious, with no apparent signs of a pulse or breathing. If the person's breathing has stopped or appears dangerously low or shallow, begin cardiopulmonary resuscitation (CPR) immediately if you're trained.
Share body heat. To warm the person's body, remove your clothing and lie next to the person, making skin-to-skin contact. Then cover both of your bodies with a blanket.
Provide warm beverages. If the affected person is alert and is able to swallow, have the person drink a warm, nonalcoholic beverage to help warm the body.
What not to do
Don't apply direct heat. Don't use hot water, a heating pad or a heating lamp to warm the person. Instead, apply warm compresses to the neck, chest wall and groin. Don't attempt to warm the arms and 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 massage or rub the person. Handle people with hypothermia gently because they're at risk of cardiac arrest.
Don't provide alcoholic beverages. Alcohol lowers the body's ability to retain heat.
What a doctor may do
A doctor will be able to take steps to warm the body from the inside out, if necessary. One method may involve giving the person warm fluids intravenously.
In severe cases of hypothermia, a process called hemodialysis may restore normal body temperatures quickly. Hemodialysis is a medical procedure that removes extra fluid, chemicals and wastes from the blood by filtering the blood through an artificial kidney. It's often used in people with kidney failure. In a hypothermia situation, the blood is removed purely to warm it rapidly outside the body and then have it returned to the body.
Prevention
For people most at risk of hypothermia — people who are older, who have mental or physical impairments, or who are homeless — community outreach programs and medical and social support services can be of great help. Identifying and checking in on vulnerable people and groups, avoiding prolonged exposure to the cold, and ensuring adequate heating are good steps to take toward hypothermia prevention. Monitoring bracelets may provide assistance for people who have a tendency to wander from home.
Avoid excessive alcohol consumption and the use of illegal substances, because these may increase your risk of hypothermia. Also, don't drink alcohol and operate a boat or other watercraft. Alcohol can impair your ability to navigate the waters, increasing your risk of an accident and of falling into cold water.
Staying healthy 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. Mittens are more effective than gloves are because mittens keep your fingers in closer contact with one another.
Overexertion. Avoid activities that would cause you to sweat a lot. The combination of wet clothing and cold weather can give you chills.
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 more body heat than cotton does.
Dry. Stay as dry as possible. In the winter, pay special attention to places where snow can enter, such as in loose mittens or snow boots.
During cold-weather months, keep emergency supplies in your car in case you get stranded. Supplies may include several blankets, matches, candles and some foodstuffs, such as granola bars or crackers. A cell phone also can come in handy. If your car is stuck in a snowbank, be careful about leaving the engine running, because infiltration of carbon monoxide inside the car may pose a silent danger.
Cold-water cautions
Water doesn't have to be extremely cold to cause hypothermia. Any water that's colder than body temperature causes heat loss. Water that's colder than 70 F can quickly begin to cause hypothermia. 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 allowing you to float without using energy and providing some insulation.
Don't panic. If you're unable to swim to safety, stay calm. Unnecessary movements require you to exert extra energy and lose body heat.
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. Buckle, button and zip up your clothes. Cover your head if you have a hood. The layer of water between your clothing and your body will be warmed and help insulate you.
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 expends extra energy, lowers body temperature and can shorten survival time.
By Mayo Clinic Staff
Jun 8, 2007
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