The information provided here is for educational purposes. It is not a substitute for specific training. Scientific research continues to change society’s understanding and treatment of hypothermia. Minnesota Sea Grant assumes no liability for an individual's use of or reliance upon the material offered on the Minnesota Sea Grant Web site.
- What is hypothermia?
- Who is at risk for developing hypothermia?
- How long can a person survive in cold water?
- Improving chances of survival in cold water
- Preventing hypothermia
- Hypothermia symptoms
- Treating hypothermia
- Hypothermia Symptom and Treatment Chart
- The body-to-body rewarming controversy
- Alcohol consumption increases the odds of developing hypothermia
- What is the mammalian diving reflex?
- What is the torso reflex?
- A True Story! So C-C-C-Cold
- Stayin' Alive Hypothermia Video
What is hypothermia?
Hypothermia is a physical condition that occurs when the body’s core temperature falls below a normal 98.6° F (37° C) to 95° F (35° C) or cooler. Think of hypothermia as the opposite of heat stroke. Cold water dangerously accelerates the onset and progression of hypothermia since body heat can be lost 25 times faster in cold water than in cold air. Hypothermia affects the body's core – the brain, heart, lungs, and other vital organs. Even a mild case of hypothermia diminishes a victim’s physical and mental abilities, thus increasing the risk of accidents. Severe hypothermia may result in unconsciousness and possibly death. About 600 people in the U.S. die of hypothermia each year.
Who is at risk for developing hypothermia?
Elderly people, homeless people, and those under the influence of alcohol or drugs are particularly vulnerable to hypothermia. Children and people with certain health disorders are also susceptible. So are outdoor enthusiasts who spend time boating, fishing swimming, hiking, or skiing. How quickly a person becomes hypothermic depends on a variety of factors, including personality, behavior, physical condition, clothing, and environmental factors. Everyone reacts differently to the cold, even under the same conditions. Generally, children lose body heat more quickly than adults and thin people lose body heat faster than overweight people. People dying of hypothermia in the U.S. are likely to be older than 60, male, unmarried, and living in Alaska, Montana, or Wyoming.
How long can a person survive in cold water?
|Water Temperature||Expected Time Before Exhaustion or Unconsciousness||Expected Time of Survival|
|32.5°||0.3°||< 15 minutes||45 minutes|
|32.5–40°||0.3–4.4°||15 – 30 minutes||30 – 90 minutes|
|40–50°||3.3–10°||30 – 60 minutes||1 – 3 hours|
|50–60°||10–15.6°||1 – 2 hours||1 – 6 hours|
|60–70°||15.6–21.1°||2 – 7 hours||2 – 40 hours|
|70–80°||21.1–26.7°||3 – 12 hours||3 hours – indefinite|
|> 80°||> 26.7°||Indefinite||Indefinite|
Minnesota’s inland lakes and streams are generally colder than 70° F in winter and spring. Water this cold always presents the danger of hypothermia. Surface water temperatures in western Lake Superior rarely exceed 70° F. Lake Superior's average surface temperature is about 40° F (4° C).
Survival depends to some extent on...
- Individual Differences
- swimming ability, body size and build, cold tolerance, shivering response, body fat, alcohol levels
- Behavioral Response
- psychological makeup, will to live, activity, posture
- Technological Factors
- clothing, flotation aides
Improving Chances of Survival in Cold Water
In cold water, conserving body heat is essential for survival and for increasing your chances of being rescued. The rate at which a body cools varies with body size, age, gender, water and air temperature, waves, wind, water currents, and other factors.
Different situations affect survival time for an average-sized, lightly clothed adult in 50° F (10° C) water:
|Situation & Equipment||Predicted Survival Time in 50° F Water|
|Without flotation device|
|Drown proofing||1.5 hours|
|Treading Water||2 hours|
|With personal flotation device (e.g. vest or collar-type PFD)|
|Holding Still||2.7 hours|
|H.E.L.P. position||4 hours|
|Huddling with others||4 hours|
|With hypothermia prevention equipment|
|Insulated flotation jacket (float coat)||3 – 9 hours|
Maximize your chances of surviving by:
- Wearing a personal flotation device (PFD)
- Adopting a survival position
- Keeping clothing on
- Getting as much of body out of the water as possible
- Remaining still and in place UNLESS a floating object, another person, or the shore is nearby
- Keeping a positive mental outlook (a will to survive really does matter)
Swimming isn't recommended unless there is little chance of being rescued and shore is less than a mile away. Putting on a PFD after falling into cold water is almost impossible – SO WEAR IT. If you find yourself in cold water without a PFD and nothing to climb onto, tread water. Traditional drown-proofing by repeatedly lowering your head into the water and floating speeds up heat loss.
Savvy outdoors enthusiasts know that insulating critical heat loss regions (head and neck, sides of chest, armpits, and groin) forestalls hypothermia, frostbite, or simple cold discomfort. Layering appropriate fabrics helps preserve body heat, also. Kayaker and freelance writer, Tim Sprinkle, has three rules for dressing for a potentially chilly day outdoors:
- No cotton. When wet it is worthless as an insulator and heavy.
- "Wick, warmth, and weather." Wear a wicking fabric next to your skin, insulating layers of fleece or wool, then an outer layer made of windproof, watertight materials.
- No cotton; seriously.
Clothing made of modern watertight materials like nylon and Gore-Tex are good for keeping warmth in and cold water out. However, they require carefully selected underclothing since the garments may not have built-in insulation. If flotation materials are not used, then wear a PFD in addition to watertight clothes.
Wear a personal flotation device (PFD). For the greatest protection against hypothermia, insulate the critical regions of your body with specifically designed PFD. A vest PFD offers more protection than a collar-type, and will improve your chances of survival. Insulated flotation jackets protect more of your body than vest or collar-type PFDs. A hood protects the head and neck area, and a removable seat panel reduces heat loss in the groin area.
Regardless of what you use to prevent hypothermia – life vest, float coat, industrial work suit, survival suit, or drysuit – flotation and insulation are important in increasing your survival time. PFDs designed to prevent hypothermia are recommended for anyone who spends time on or near cold water. To increase your visibility in the water, add reflective tape to your PFD. A strobe light, whistle, or emergency position indicating radio beacon (EPIRB) will increase your chance of being rescued.
Minnesota requires boaters to carry a Coast Guard-approved PFD for each person in the boat. Even though the law requires merely having a PFD in the boat, wearing it is recommended. Trying to put on a PFD after falling into cold water is almost impossible.
The more body area you keep out of the water, the better your chances for survival. The drown proofing technique of repeatedly lowering your head into the water and floating causes substantial heat loss, and is not recommended in cold water. If possible, climb onto your capsized boat or pull yourself out of the water onto a floating object to increase your chances of survival. If you have no personal flotation device and nothing to climb onto, tread water.
The more energy you use in cold water, the more your body cools off. If you cannot climb out of the water, conserve body heat by remaining as still as possible and reducing the amount of your body exposed to the water. Protect your critical heat loss regions: the head, sides, armpits, and groin. Do not swim unless shore, a raft, or an overturned boat is nearby. Swimming accelerates heat loss. Remaining still in the water increases your survival time.
The Heat Escape Lessening Posture (H.E.L.P.) can be used only if you are wearing a personal flotation device. Hold your arms tightly against your sides and across your chest, pull your legs together and up toward your chest. The H.E.L.P. position can be difficult to maintain due to wave conditions, PFD design, and body size. A group of two or more people wearing PFDs can huddle together to conserve body heat, offer moral support, and provide a larger target for rescuers.
When you first fall into cold water you gasp (torso reflex). Next, your skin begins to cool, and your body constricts surface blood vessels to conserve heat for your vital organs. Blood pressure and heart rate increase. Muscles tense and shiver; this produces more body heat, but results in a loss of dexterity and motor control. As your body’s core temperature drops further, blood pressure, pulse, and respiration rates all decrease.
As conditions worsen, your mental attitude and level of consciousness change. Resisting help and acting irrational or confused are common indicators of hypothermia. As your core temperature drops dangerously low, you become semiconscious, then unconscious. Stress, shock, and low core temperatures may cause cardiac and respiratory failure.
Hypothermia sneaks up on you, so you probably aren't the best judge of whether or not you are hypothermic.
Signs that a person is nearing a hypothermic state include shivering, poor coordination, and mental sluggishness. As hypothermia progresses, shivering ceases, coordination is severely impaired, and confusion is coupled with incoherence and irrationality. Severely hypothermic people have icy skin. Extreme lethargy merges with unconsciousness and they might appear dead.
Since each individual reacts differently, the severity of hypothermia is best measured by taking a core temperature reading using a rectal thermometer. Oral measurements do not accurately measure changes in core temperature.
First aid goals include:
- preventing further heat loss,
- re-warming the victim,
- quickly getting professional medical help as needed.
Read about the body-to-body rewarming controversy.
Minimize the victim’s physical exertion when removing her or him from cold water. Rescuers may have to enter the water to get the victim. Once out of the water, gently remove wet clothing and cover the person with dry clothing or blankets. Protect the victim from wind, especially around the head and neck. Move them to a warm environment if possible and avoid re-exposure to the cold. Warm compresses and warm (not hot) liquids that are non-alcoholic and non-caffeinated also help to restore heat.
Other recommendations include applying hot water bottles (maximum temperature of 115° F (46° C)) or hot, damp cloths to the victim’s head, neck, trunk, and groin (change the water periodically to ensure a constant temperature). Exhale into the victim’s face as s/he inhales. Immerse the victim’s trunk but keep the arms and legs out of a warm bath (maximum temperature of 115° F (46° C)).
If you are helping a hypothermic person, be gentle; internal organs are sensitive to physical shocks. The victim should remain as inactive as possible so blood from their cold extremities won't reach their core too quickly. A cold heart is particularly susceptible to ventricular fibrillation. During all first aid efforts, watch for changes in the victim’s temperature and vital signs. "After drop" is a danger when re-warming hypothermia victims because cold blood in the extremities returns to the body core, lowering the core temperature further.
Hypothermia victims with moderate to critical symptoms should see a medical professional as soon as possible.
Hypothermia Symptom and Treatment Chart
The following general procedures assume a rescuer has no special medical training or equipment:
|Mild Case: Body temperature is 97 - 93° F (36.1 - 33.9° C)|
|Moderate Case: Body temperature is 93 – 90° F (33.9 – 32.2° C)|
|Severe Case: Body temperature is 90 – 82° F (32.2 – 27.8° C)|
|Critical Case: Body temperature is less than 82° (< 27.8° C)|
The body-to-body rewarming controversy
Some medical professionals and rescue personnel recommend rewarming mildly hypothermic victims in the field with body-to-body contact (in other words, by sharing body heat). However, research suggests that this technique may not be beneficial. The rationale comes from the fact that the person offering up their body heat is giving about as much heat as they are taking away by restricting the victim’s shivering response. And, the heat donor becomes colder in the process.
In a study1 evaluating whether body-to-body rewarming would enhance the recovery of a mildly hypothermic subject, researchers found that sharing body heat was approximately as effective as letting a person rewarm from their own shivering.
In a different study2, researchers simulated severe hypothermia by suppressing a victim’s shivering response. In cases where a person cannot shiver themselves back to normal, they report that body-to-body rewarming yields a faster recovery than letting a victim passively rewarm but it is significantly less effective than applying a heater and a rigid cover to the victim’s chest.
Alcohol consumption increases the odds of developing hypothermia
Alcohol consumption can speed the onset and progression of hypothermia. Alcohol impairs motor skills, magnifies the torso reflex, and affects clear thinking. As the alcohol level in a person's body increases, coordination abilities decrease. At high doses, alcohol damages thermoregulation, which lowers the body's resistance to cold water.
What is the mammalian diving reflex?
The mammalian diving reflex is an innate response to cold water exhibited by mammals – including humans. Cold water contacting the face triggers the reflex, which shunts blood and available oxygen to the heart and brain. It lowers the heart rate and limits blood circulation to all but the body’s core. Water warmer than 70° F does not cause the reflex, and neither does plunging non-facial body parts into cold water. Children younger than 3 years old exhibit the reflex more dramatically than adults. The diving reflex enables some children to survive for an unusually long time in frigid water.
Because of the diving reflex, near-drowning victims have been revived after as long as one hour under cold water. The chances for surviving depend on water temperature (colder is better), length of time under water, age of the person (younger is better), and rescue efforts.
What is the torso reflex?
The torso reflex (also known as the gasp reflex or inhalation response) is a physiological reaction – an involuntarily gasp – that happens when a person suddenly enters cold water. The reflexive sucking in of air is a way for the body to rapidly increase oxygen intake into the lungs as a means of increasing survival.
Some reported drowning victims don't die as a result of poor swimming skills or the effects of hypothermia, but from the torso reflex. Occasionally the torso reflex causes victims to inhale water. A person can also die from cardiac arrest brought on by sudden entry into cold water.
A True Story! So C-C-C-Cold
Bob Sopoci thought he was a goner. On an early April evening, this Grand Marais, Minn., resident and his fishing buddy fell through the ice of a northern border lake. After losing his shoes and gloves while struggling to get out of the water, Sopoci spent that night huddled on the ice with his equally cold, exhausted friend. By dawn, they were hallucinating. When they resumed their slow and painful attempt at exodus, the ice, which just one week earlier supported trucks, again gave beneath their weight. This time they said their goodbyes. Death didn't claim them, however. Another half-day of tribulation, which included periods of disorientation, unconsciousness, and the first signs of kidney failure, ended with the seasoned outdoorsmen rescuing each other. Not everyone is so fortunate.
In the weeks following Sopoci's 24-hour ordeal, all the skin sloughed off his swollen arms and he took medication to ease the excruciating pain of frostbite. Sopoci's experience brought home the fact that clothing counts and to let someone know of your plans. He also commented wryly, "Travel with a friend, and always let them go first."
Stayin' Alive Hypothermia Video
In this video from the Minnesota Sea Grant College Program, tips on how to prevent hypothermia are offered as viewers watch an individual take "the polar bear plunge" for a charity event.
- Hypothermia Gives Me the Shivers (5:39), Aired 2/17/10
1.1 MB mp3 | Stream
- Hypothermia 101 (Dec. 2009 Seiche newsletter)
- Mayo Clinic
- Centers for Disease Control and Prevention
- Pozos, R. and L. Wittmers (eds.). 1983. THE NATURE AND TREATMENT OF HYPOTHERMIA. 1983. University of Minnesota
- The work of Dr. Gordon Giesbrecht.
1Giesbrecht, G. G., D. I. Sessler, I. B. Mekjavic, M. Schroeder and G. K. Bristow. 1994. Treatment of mild immersion hypothermia by direct body-to-body contact. Journal of Applied Physiology 76(6) 2373-2379.
2Hultzer, M.V., X. Xu, C. Marrao, G. Bristow, A. Chochinov, G. G. Giesbrecht. 2005. Pre-hospital torso-warming modalities for severe hypothermia: a comparative study using a human model. Canadian Journal of Emergency Medicine 7(6): 378-386.