Hypothermia
Keeping warm and safe in the cold
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First published: 29.Oct.2024
Overview
Cold weather increases the risk of suffering from hypothermia. This is a serious medical condition that can cause death. Its complications can provoke frostnip and frostbite. In this article we describe it, its causes, symptoms, treatment, and how to prevent it.
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What is Hypothermia?

When the body loses more heat than it absorbs or creates it enters a state called hypothermia.
The word was coined in Britain in the 1880s and combines the Greek words hypo which means "below", Thermē, meaning heat, and the suffix "-ia" that refers to a disease or medical condition.
Medically, hypothermia takes place when the body temperature falls below 35°C. It affects all organs. (1)
Causes
The body's temperature is normally constant and oscillates between the normal values of 36.5 and 27.5°C. There is a balance between the heat generated by the body and the heat it loses to the surroundings. This thermal equilibrium can be altered when one of these factors change: too little heat is produced or more heat is lost.
Inadequate internal body heat generation (or thermogenesis), extreme external cold temperatures or a combination of both can disrupt the thermal balance of a body.
Hypothermia is a serious condition that can cause death if not treated immediately. (1)
Heat Balance Science
Newton's law of cooling states that the amount of heat lost to the environment is proportional to the "heat transfer coefficient" (h) and to the difference of temperatures between the environment (Tenv) and the body (Tbody) called ΔT.
The lower the outside temperature is, the greater will be ΔT. Causing a larger heat loss.
The greater the heat transfer coefficient "h", the greater the loss of heat.
The lower the external temperature, the higher the heat lost by the body:
Qlost = h * (Tbody - Tenv)
This is why colder external temperatures cause heat loss. The heat transfer coefficient is low for insulating clothing, but it grows with light fabrics. It grows considerably when the clothing items are wet, or when heat loss is increased by higher convection due to the wind.
The body loses heat through radiation (bare skin), irradiating heat into the surroundings, by conduction, contact between the body and the environment and convection, caused by a fluid (water or air) flowing past the body. Some heat is lost through respiration as you breathe, and by evaporation as your sweat evaporates to cool you.
Internal heat production can drop due to malnutrition, age, drops in blood sugar levels and other medical conditions.
Hypothermia is quite frequent in cold regions during the winter months. But it can also happen in temperate climates under certain conditions (cold, wind, inadequate clothing and chill factor).
Tool for calculating Wind Chill
The wind causes a forced convection (like when you blow on a cup of coffee or a bowl of soup, to cool it) over the body's surface and removes heat much quicker than in windless conditions. The body senses this as a much colder temperature than the one marked by the thermometer.
Number of Cases
Every year there are between 700 and 1,500 deaths related to hypothermia in America. The mortality due to moderate to severe hypothermia is around 50%. The total number of cases is unknown. (1)
Most affected are adults between 30 and 49 years old, and it affects ten times more men than women. Perhaps due to the greater presence of men outdoors during the cold period.
How hypothermia develops and progresses
You can get hypothermia because the surroundings are too cold:(4)
- You are not well dressed in cold weather.
- Your home is too cold.
- You stay outdoors in the cold for too long.
- You fell into cold water.
- Your clothes are wet (even sweating under warm clothes is a problem) and you get cold.
Once the cold becomes evident, the body must maintain its core temperature. So, sensing it is growing cold due to heat loss, it increases its metabolism (energy output). This implies a higher breathing reate and heart rate. The body will also shiver to warm itself by rapidly contracting and relacing muscles to generate heat.
If heat loss continues, it overwhelms the body and it can disrupt the shivering mechanism. As time passes all organ systems start shutting down (metabolic, neurologic and cardiac). If unchecked it will cause death.
Vulnerability increases when blood circulation is impaired by cardiovascular disease, alcohol intake, exhaustion, and hunger. (1), (2)
Prevention of Hypothermia
Education is the key. People should know how to avoid hypothermia. There are some simple steps to prevent it. (1)
- Stay indoors as much as possible during cold weather spells.
- Homes should be kept warm and safe (Carbon monoxide and smoke detectors), insulated and draught-proofed.
- When you go outdoors use proper warm clothing to retain body heat and protect it from cold and wet conditions. This includes footwear, hats, gloves.
Use multiple layers, avoid constricting gloves, shoes, socks and wrist bands. - If your clothes become wet either by rain, snow, falling into water, or sweating, change into dry clothing.
- Vulnerable people should be protected: the infirm, babies, toddlers and young children, the elderly as well as people with mental health issues should always wear warm clothing. Hypothermia-causing medicine should be kept out of their reach.
- Avoid solitary activities that increase the chance of hypothermia while being alone (skiing, snowboarding, mountaineering, rafting, boating) in cold places.
- When outdoors during cold periods carry spare dry clothes, and gear to light a fire and keep warm as well as lightweight energy-dense foods (granola or protein bars).
- If weather worsens while outdoors, find a sheltered spot and get out of the wind. Try to stay warm.
- Your body requires ´plenty of energy to keep warm. Eat plenty of foodwith carbohydrates as they release quick energy. If you will be outdoors for a long period of time eat a meal with fat and protein to keep you going for many hours.
- Fluids: your body requires fluids to operate normally, even if it is cold and you don't feel thirsty, you lose water when you breathe and sweat; avoid dehydration.
- If you suspect you are being affected by hypothermia, put on warm clothes, remove wet ones, stay indoors in a warm place, eat carbohydrates, drink warm fluids. Move your body to warm your core.

Warm Clothes
Multiple thin layers insulate better than one thick layer of the same thickness because they trap air, an insulator between the fibers.
Avoid using cotton in cold weather, specially your underwear. Cotton absorbs moisture (pespiration) and keeps it next to your skin, increasing heat loss by conduction, making you cold.
Wear an inner garment that wicks the sweat away from the skin (wool, polyester, etc). Over this wear insulating layers to keep the body heat in, like fleece, wool, microfiber, down.
The outer layer should be waterproof and repel snow, rain and also block the wind. Breathable fabrics help the sweat evaporate and not wet you.
Face, head, neck, feet and hands also require protection. Use a warm hat. face mask, neck warmer or scarf, gloves and or mittens, waterproof shoes or boots with thick soles.
Layered clothing allow you to remove items as you warm up during your activity and avoid sweating and getting wet.
Hypothermia Symptoms
As the inner temperature of your body drops -even if it only a few degrees- the brain and internal organs stop functioning correctly, causing symptoms that are easy to detect. Look out for the following: (2), (4)
- Uncontrolled shivering, chattering teeth.
- Slow. slurred or unclear speech.
- Fatigue and extreme tiredness.
- Slow breathing.
- Mental confusion, loss of the ability to think clearly.
- Stumbling when attempting to walk
These symptoms are known as the "Umbles:" stumbles, bumbles, grumbles, and mumbles. - Loss of consciousness.
- Pale, cold, and dry skin; Skin and lips may turn blue or grey (check palms or foot soles in dark skinned people).
In babies, look out for these signs: they are cold to touch, floppy and unusually quiet; or sleepy. They may refuse to feed.
What to do if someone has hypothermia
Hypothermia is a medical emergency that needs to be treated in hospital.
If you believe that someone has hypothermia, call for medical help immediately. While waiting for the help to arrive, do the following. (4)
- Move the person out of the cold as fast as you can. Indoors, or if that is not possibly, find a sheltered place, out of the wind.
- Place the person close to a warm -not hot- source of heat.
- Remove wet clothing and wrap the person in a blanket, dry towel or a sleeping bag. Cover their head, hands and feet to avoid further heat loss.
- Lie under the covers next to the person to transfer your own body heat to them; if possible, someone else should lie on the other side.
- If the person is fully awake, try to give them a warm -not hot- broth, soup or sugary beverage (hot chocolate, milk) do not give them alcoholic drinks.
- Infants: wrap the baby inside your own clothing against your warm skin.
- Keep them awake until medical help arrives.
Things you shouldn't do to a person with hypothermia
There are some things you should not do because they can worsen the condition. (4)
- Don't use a hot water bottle, heat lamp or hot bath to warm the person.
- Don't rub their legs, feet, hands or arms.
- Don't give them alcohol to drink.
- Don't warm a person too fast.
Semi-consciousness or unconsciousness
If a person becomes unconscious due to hypothermia seek immediate medical help. If they suffer a heart attack call for medical assistance and then apply CPR.
Treatment
Medical treatment will be provided at the hospital and it will focus on preventing further heat loss and quickly rewarming the patient while ensuring circulation and breating are under control.
Frostbite is a complication that arises from hypothermia and and it will be addressed by the health care provider.
Frostbite
As the body undergoes hypothermia, it struggles to keep the core temperature constant, to protect your vital organs. To do this, it slows the blood circulation in your limbs and face. So toes, fingers, feet, hands, nose, ears, cheeks receive less flow of blood. Since the blood is at body temperature, the lower flow reduces the heating effect caused by circulation. The skin and tissues in these areas become colder, and oxygen deprived. This increases the risk of frostbite.
Frostnip
The first signs of frostbite are known as "frostnip:" (3)
The skin feels cold and red. It may also turn white. There is prickling, tingling, stinging and numbness.
Get out of the cold, put on warm clothing, warm the frostnipped area: remove tight jewelry, rings and constricting clothing to ensure adequate circulation. Warm fingers under your armipits and your nose with the palm of your warwm hand. NEVER rub a frostnipped area.
If the person worsens after attempting to warm up frostnip, and frostbite has set in, seek immediate medical attention, NEVER rewarm frostbite on your own it can only worsen things. (3)
Frostbite is serious, it can lead to limb loss if not treated quickly. Secondary infection may set in causing gangrene.
References and Further Reading
(1) Duong H, Patel G. . (2024). Hypothermia.[Updated 2024 Jan 19],. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK545239/
(2) Public Health — Seattle & King County, (2024). How to treat and prevent hypothermia .Seattle, WA. USA. Accessed: 10.29.2024
(3)(3) Linda J. Vorvick. David C. Dugdale, Brenda Conaway, (2022). How to prevent frostbite and hypothermia. A.D.A.M. Medical Encyclopedia [Internet].Review Date 8/11/2022. Accessed: 10.29.2024
(4) NHS, (2023). . Page last reviewed: 09 June 2023. Accessed: 10.29.2024
About this Article
Hypothermia, A. Whittall
©2024 Fit-and-Well.com, 29.Oct.2024. Update scheduled for 29 Oct. 2027. https://www.fit-and-well.com/health/hypothermia.html
Tags: hypothermia, winter, frostbite.