Hypothermia: What Published Guidance Supports

Key takeaways

• Definition: body temperature below 95°F (35°C)
• Signs in adults: shivering, exhaustion, confusion, fumbling hands, memory loss, slurred speech, drowsiness
• Most useful single change: Dress in layers and cover your head, hands and feet in cold weather.
• Commonest mistake: Drinking alcohol to "warm up".
• See a doctor if any of the signs under "When to speak to a doctor" below apply to you.

What it is

A dangerously low body temperature caused by losing heat faster than the body can produce it. It sits within Weather Safety. The table below gives the figures guidance actually works from.

The numbers, in one place

What helps

The advice below comes straight from the guidance cited at the foot of this page.

• Dress in layers and cover your head, hands and feet in cold weather
• Change out of wet clothes as soon as possible
• Warm the center of the body first: chest, neck, head and groin
• Give warm, non-alcoholic drinks only if the person is fully alert

What to avoid

What to steer clear of, and why it catches people out.

• Drinking alcohol to "warm up"
• Warming the arms and legs before the center of the body
• Giving drinks to someone who is unconscious

In depth

Your body produces heat constantly through metabolism and muscle activity, and loses it to the surroundings through the skin and breath. When heat loss outpaces heat production for long enough, core temperature falls. Below 95°F (35°C), the brain, heart and other organs begin to slow down. That is hypothermia. Water and wind speed up heat loss dramatically, which is why wet clothing or a fall into cold water can cause hypothermia even when the air does not feel especially cold.

In mild hypothermia the body fights back hard. Blood vessels in the skin narrow to keep warm blood in the core, and muscles shiver to generate heat. As temperature falls further, shivering weakens and may stop, thinking becomes slow and confused, and judgment fails. People may stumble, slur their words or even remove clothing, so they often cannot recognize what is happening or ask for help. This is why companions, family members and bystanders play such an important role.

Severe hypothermia affects the heart's rhythm and can lead to cardiac arrest. Yet the cold also protects the brain to some degree by reducing its need for oxygen, and people have recovered after long periods of very low body temperature. For this reason, emergency teams continue care and rewarming even when a person appears lifeless. Careful handling matters, because a very cold heart is sensitive, and rough movement can trigger dangerous rhythms.

Signs and symptoms

• Constant, uncontrollable shivering in the early stage
• Pale, cold skin, especially on the belly and chest rather than just hands and feet
• Slowed breathing and heart rate as temperature drops
• Poor coordination, stumbling or trouble with simple tasks like zipping a jacket
• Apathy, poor judgment or behavior that seems out of character
• Shivering that stops while the person is still cold, a sign of worsening hypothermia

Causes and risk factors

• Wet clothing from rain, snow, sweat or falling into water
• Wind, which strips heat from exposed skin
• Cold homes, especially when heating is turned down to save money
• Alcohol and some drugs, which widen blood vessels and dull awareness of cold
• Older age, very young age and low body fat
• Conditions such as an underactive thyroid, diabetes, stroke, dementia and malnutrition
• Exhaustion, injury or being unable to move, for example after a fall

How it is checked

Hypothermia is suspected from the setting and the person's signs: a cold environment, cold skin on the trunk, shivering or confusion. Standard home thermometers often cannot read very low temperatures accurately, so a reading may not show how cold the person really is. If someone is confused, very drowsy or not shivering despite being cold, treat it as serious and call 911.

In the emergency room, staff measure core temperature with a special low-reading thermometer, often rectally or through a probe in the esophagus or bladder. They monitor the heart rhythm and check blood tests including blood sugar, salts, kidney function and signs of infection or drug and alcohol use. They also look for injuries, frostbite and medical problems that may have led to the hypothermia.

Treatment and support options

First steps for anyone

Move the person into a warm place if you can, handling them gently. Remove wet clothing and replace it with dry layers, then wrap them in blankets, including the head and neck, with insulation underneath them as well. Skin-to-skin contact under loose layers can help. Warm the chest, neck, head and groin first. Call 911 for anything beyond mild shivering in an alert person.

Warm drinks and food

If the person is fully alert and can swallow safely, warm, sweet, non-alcoholic drinks and food give the body fuel to make heat. They are not a substitute for getting warm, but they help. Never give anything by mouth to someone who is drowsy, confused or unconscious, because they could choke.

Hospital rewarming

For moderate or severe hypothermia, hospital teams use active rewarming, such as forced warm-air blankets, warmed fluids into a vein and warmed, humidified oxygen. In the most severe cases, specialized centers may use machines that warm the blood directly. The heart rhythm is watched closely throughout, because rewarming itself can trigger problems.

If there is no pulse

Check carefully for breathing and a pulse for up to a minute, because both can be very slow and faint. If there are none, start CPR and continue until emergency help arrives. Emergency teams may continue resuscitation for a long time, since recovery after severe hypothermia is possible.

Prevention

• Dress in layers, with a moisture-wicking base layer and a wind- and water-resistant outer layer
• Carry spare dry socks, gloves and a hat when hiking or working outdoors in winter
• Keep your home heated, and seek help with heating costs if money is tight
• Tell someone your route and return time before outdoor trips
• Check in on older relatives and neighbors during cold snaps and power outages

Day to day

Most people with mild hypothermia recover fully once warmed. After a more severe episode, it is common to feel tired and weak for some days, and you may be monitored for heart, kidney or lung effects. If you were hurt, such as by a fall that left you on the floor, recovery from the injury may take longer than the hypothermia itself. Ask what follow-up you need before leaving the hospital.

Think about what led to the episode and what would prevent it next time. That might be a better heating setup, a medical alert device for someone who lives alone, a review of medicines that cause drowsiness, or changing outdoor plans when wind and rain are forecast. If cost is a barrier to heating, the Low Income Home Energy Assistance Program and local utility programs may help.

For specific groups

Babies

Babies lose heat quickly and cannot shiver well. A baby with hypothermia may have bright red, cold skin and very little energy. Keep the room comfortably warm and dress them in layers, but do not use loose blankets in the crib; a wearable blanket is safer.

Older adults

Hypothermia can develop indoors in an older adult over hours or days in a cool home, especially with illness, poor nutrition or certain medicines. Confusion may be mistaken for dementia. Keeping the thermostat at a safe level is essential.

People who drink heavily or use drugs

Alcohol makes you feel warmer while actually increasing heat loss, and it dulls the urge to seek shelter. People who fall asleep outdoors after drinking are at high risk. Friends should make sure everyone gets home safely in cold weather.

People experiencing homelessness

Being outside for long periods, wet clothing and limited access to warm shelter put unhoused people at high risk. Many cities open warming centers and extra shelter beds during cold weather; calling 211 can help find them.

Questions to ask your doctor

• Do any of my medicines make me more sensitive to cold?
• Could a thyroid problem or other condition be making me feel cold all the time?
• What indoor temperature is safe for me or my older relative?
• After this episode, do I need any heart, kidney or blood tests?
• What signs should prompt me to call 911 rather than warm up at home?
• Would a medical alert device be a good idea for me?

More questions, answered

Can you get hypothermia indoors?

Yes. Older adults, babies and people who are ill can develop hypothermia in a cold house, even when the temperature does not seem extreme. Long exposure to mild cold can be enough. Keeping the home heated and wearing layers indoors help prevent it.

Should I rub someone's arms and legs to warm them up?

No. Rubbing the limbs does little to warm the core and can damage cold skin. Focus on warming the center of the body first, with dry clothing, blankets and warm packs on the chest, neck, armpits and groin, and handle the person gently.

Is a hot bath a good way to rewarm?

For a mildly cold but alert person, a warm, not hot, shower or bath can be comfortable once wet clothing is off. For anyone with more than mild hypothermia, call 911 instead, because rapid warming of the skin can cause blood pressure to drop and strain the heart.

Why does a hypothermic person stop shivering?

Shivering uses a lot of energy and stops as the body runs low on fuel or as temperature falls further. Stopping shivering while still cold is a warning sign that hypothermia is getting worse, not better.

How fast can cold water cause hypothermia?

Water draws heat from the body much faster than air at the same temperature. In cold water, the first danger is the gasp and fast breathing of cold shock, then muscle weakness that makes swimming hard. Hypothermia follows. Wearing a life jacket is the most important protection.

Is it true that you are not dead until you are warm?

Emergency teams follow this principle because very cold bodies can survive conditions that would otherwise be fatal. They will often continue CPR and rewarming for a long time. As a bystander, start CPR if there is no pulse and keep going until help arrives.

Related topics

• CPR and Defibrillation: What the Evidence Actually Says (Emergency Care)
• Sun and Heat Abroad: What the Evidence Actually Says (Travel Health)
• Dry Skin: Sorting the Evidence From the Noise (Skin Health)
• The Evidence on Fever, Without the Hype (Immunity)

Where to go next

• Popular Beliefs About Hypothermia, and What Is Actually Published
• Hypothermia: A Beginner-Friendly Start
• Hypothermia — the reference entry
• Weather Safety: The Complete Guide
• Frostbite: What Published Guidance Supports
• Wildfire Smoke: What Published Guidance Supports

When to speak to a doctor

Call 911 if a person's temperature is below 95°F or they are confused, very drowsy or unresponsive. If the person has no pulse, start CPR while waiting for help.

Where this comes from

• CDC — Preventing Hypothermia
• National Institute on Aging — Cold Weather Safety for Older Adults

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.