Stay safe—and know the signs to watch for—if you're spending time outdoors in subzero temperatures.

As we head into the winter months, it's important to remember that extreme temperatures of any kind are possibly damaging to the human body. While very hot temperatures can cause a range of issues—heat stroke, heat exhaustion, and heat cramps, for example—extremely cold temperatures can be just as harmful.

One major concern in extreme cold is frostbite, Stephanie Lareau, MD, assistant professor of emergency medicine at Virginia Tech Carilion School of Medicine, tells Health. But despite its relative frequency, there’s a lot people don’t know about this condition, Dr. Lareau says. Here’s what everyone needs to know, and how you can protect yourself in the cold.

What is frostbite?

The Centers for Disease Control and Prevention (CDC) explains that frostbite is a type of injury caused by freezing, and it leads to a loss of feeling and color in the affected areas (mainly the nose, ears, cheeks, chin, fingers, and toes). It happens when blood flow to those extremities slows down, which ultimately results in freezing.

But it doesn't occur all at once, Dr. Lareau says—it can actually sneak up on people who are spending prolonged amounts of time outdoors. You may also have a greater chance of developing frostbite if you have poor blood circulation or aren't properly dressed for cold temperatures. Certain medications, alcohol use can also predispose people to frostbite, she says.

Ultimately, people with frostbite start to lose their fine motor skills and become increasingly uncoordinated, Dr. Lareau says. Thankfully, she adds, most people will recognize the beginning stages of frostbite and have time to seek warmth and stop the process.

What are the symptoms of frostbite, and what does it look like?

“The first warning signs that you are at risk for frostbite is when body parts become cold,” says Dr. Lareau. “This is typically followed by burning and stinging, and then the body parts start to lose sensation and feel like pins and needles. This is followed by numbness.”

The CDC also says that frostbite can present in the following ways:

  • A white or grayish-yellow skin area
  • Skin that feels unusually firm or waxy
  • Numbness

Frostbite severity isn’t always obvious when looking at an affected body part, says Dr. Lareau. Initially, the extremity will first look red—a stage that doctors call “frostnip,” she says.

As frostbite progresses, the skin starts to look pale. “That’s when you need to become worried, get out of the cold, and seek medical treatment,” she says. In late stages, a frostbitten body part can become covered in blood blisters or even turn black. Sometimes, the CDC adds, a person who has frostbite may not know they have it until someone else points it out because the frozen parts of their body are numb.

woman health frostbite
Credit: John van Hasselt - Corbis/Getty Images

How fast can frostbite occur?

The time it takes to develop frostbite depends on the temperature and windspeed, and the National Weather Service offers a handy Wind Chill Chart to help people determine what (and how long) is dangerous.

When the temperature is 0 degrees with 15 mile-per-hour winds, for example, frostbite can occur in about 30 minutes of exposure. But on very windy days with subzero temperatures, says Dr. Lareau, it can happen in as little as five minutes.

Is frostbite ever fatal?

People don’t usually die from frostbite itself, but it can cause permanent damage to extremities like fingers and toes—which may need to be amputated. However, frostbite typically occurs along with hypothermia (an abnormally-low body temperature), which can be deadly.

Seeking medical attention as quickly as possible, and stopping the freezing process, is very important for avoiding long-term consequences from frostbite, says Dr. Lareau. “The degree of the injury really determines what sort of recovery someone will have,” she says.

How is frostbite treated?

If people suspect they’ve developed frostbite, the best thing they can do is get inside and get warm, Dr. Lareau says. However, if they’re on long expeditions or in a remote area, it’s important not to rewarm hands or feet until they can be kept warm, she warns.

“Each time freezing injury occurs, ice crystals form,” she says. “If something re-freezes, this creates more damage.” If hands are numb, she says, you also shouldn’t rub them together or warm them over an open flame, she adds, because friction causes tissue damage, and it’s easy to burn yourself when you can’t feel the heat.

At medical facilities, some clot-busting medications (like those used for stroke victims) can be used to stop or reverse some damage from severe frostbite. In remote areas, bandaging the extremity in a bulky dressing—and evacuating to a warmer, indoor area—is the best initial treatment, she says. Once indoors, it’s best to rewarm extremities in a warm-water bath. (Aim for the temperature of a hot tub, but no higher.)

But the best way to avoid damage from frostbite is to prevent it in the first place, of course: Wear appropriate clothing and keep skin covered when spending time outdoors in the cold. Pay attention to weather alerts—and to strange symptoms like tingling and numbness—to keep yourself safe.

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