Winter Hypothermia Basics: Signs and When to Call for Help

In an emergency, call 911.

If you think someone has hypothermia, call 911. CDC calls hypothermia a medical emergency, and the National Weather Service (NWS) says to call for an ambulance first when helping someone who may have it. For what to do while you wait, follow the dispatcher's instructions and the official guidance from CDC and NWS. This article covers how to recognize the signs, what raises the risk, and how to prevent hypothermia in the first place. It does not cover treatment.

What hypothermia is

The National Park Service (NPS) describes hypothermia as a condition in which your body loses heat faster than it produces it. CDC defines it as abnormally low body temperature, and NWS notes it's generally defined as a body temperature below 95°F. NWS calls it the most common winter weather killer, and Mount Rainier National Park warns that, left untreated, it can lead to unconsciousness and death.

It's not only a deep-winter problem. CDC says hypothermia can occur even at cool temperatures above 40°F if a person becomes chilled from rain, sweat or cold water.

Warning signs

In adults, CDC lists these signs:

• Shivering
• Exhaustion or feeling very tired
• Confusion
• Fumbling hands
• Memory loss
• Slurred speech
• Drowsiness

In infants, CDC lists: bright red, cold skin and very low energy.

NWS adds uncontrollable shivering, disorientation and slurred speech to its list, and NPS includes difficulty speaking and stiff muscles. NWS says to see a doctor immediately if you feel cold and sluggish or are having trouble thinking clearly.

Because confusion, memory loss and drowsiness are on the list, a person with hypothermia may not realize it. On group trips, make sure everyone knows the signs and keeps an eye on each other, not just on themselves.

Related: frostbite

Frostbite often shows up on the same trips. NWS, citing CDC, says redness or pain in any skin area may be the first sign. Other signs include a white or grayish-yellow skin area, skin that feels unusually firm or waxy, and numbness. NPS notes that frostbite usually affects the extremities and can cause a loss of feeling and color. For what to do, see the NWS and CDC pages linked below, and call 911 for severe cases.

What raises the risk

Getting wet. NWS says wet clothing makes your body lose heat much faster, and CDC lists rain, sweat and cold water as ways people get chilled. Sweat is easy to overlook on a winter hike: Mount Rainier National Park advises removing layers to avoid sweating too much, then putting layers back on when you stop to rest.

Wind. The NWS wind chill index reflects the heat your body loses to its surroundings in cold, windy weather. NWS advises seeking shelter from the wind when you're outside.

Exhaustion and hunger. CDC lists exhaustion among the warning signs, and NPS notes that physical activity and hunger can reduce your body's ability to keep itself warm.

Alcohol and drugs. CDC lists people who drink alcohol or use illicit drugs among those at higher risk. NWS says to avoid caffeine, alcohol and cigarettes in cold weather, saying they interfere with warming.

Long time outdoors. CDC includes people who stay outdoors for long periods among those at higher risk, which describes most winter campers.

Age. CDC also flags older adults without adequate food, clothing or heating, and babies sleeping in cold rooms.

Prevention: layers, food, water and shelter

Check the forecast and plan for it. Mount Rainier National Park says the best way to avoid hypothermia is to be prepared by checking the weather forecast and planning for it.

Dress in layers.

• NPS recommends layers you can easily add when you're getting cold and remove to prevent overheating.
• Choose wool or synthetic fabrics over cotton, which NPS says won't keep you warm once it's wet.
• NWS notes that air trapped between loose-fitting layers helps insulate, and CDC recommends several layers of loose-fitting clothing.
• Wear wind and rain protection that breathes, and warm, waterproof boots, as Mount Rainier advises. Its winter essentials list includes a warm hat and layered gloves.

Stay dry.

• Pack an extra set of dry clothing in a sealed bag, as NPS suggests.
• If you get wet, NWS says to change into dry clothes as soon as you can.
• NPS camping guidance recommends changing into dry clothes before bed.

Eat and drink.

• NWS recommends nutritious food, hot foods and warm drinks several times a day, and plenty of fluids.
• NPS suggests insulated containers to keep food and water from freezing.
• Mount Rainier lists a stove and fuel among its winter essentials so you can melt snow for water.

Plan your shelter and sleep system.

• NWS advises getting out of the wind.
• At camp, NPS recommends a sleeping bag matched to the temperature and conditions, and a ground pad to block moisture that would otherwise draw heat from your body. Glacier National Park calls a four-season sleeping bag and an insulated pad a must for winter camping.
• Heating a tent with a fuel-burning heater is not a safe shortcut. Never use fuel-burning appliances in enclosed spaces; carbon monoxide is odorless. See our explainer on heaters in tents.

When to call for help

Call 911 if you see the warning signs of hypothermia in yourself or someone else. CDC says hypothermia is a medical emergency, and NWS says to get medical attention right away.

Before a winter trip, find out how you would reach help where you're going, and ask the park or forest about communication options there.

Sources

• CDC, Preventing Hypothermia: https://www.cdc.gov/winter-weather/prevention/index.html
• CDC, Recognizing Hypothermia: https://www.cdc.gov/natural-disasters/psa-toolkit/recognizing-hypothermia.html
• NWS, During Extremely Cold Weather: https://www.weather.gov/safety/cold-during
• NWS Boulder, Wind Chill Safety: https://www.weather.gov/bou/windchill
• NPS, Be Winter Ready for Your Adventure: https://www.nps.gov/articles/winterweather.htm
• NPS, Mount Rainier National Park, Winter Safety: https://www.nps.gov/mora/planyourvisit/winter-safety.htm
• NPS, What to Bring — Camping: https://www.nps.gov/subjects/camping/what-to-bring.htm
• NPS, Glacier National Park, Winter Wilderness Camping: https://www.nps.gov/glac/planyourvisit/winterbccamping.htm

Last verified: November 1, 2026.