Frostbite is an injury caused by freezing of the skin and underlying tissues. In the earliest stage of frostbite, known as frostnip, there is no permanent damage to skin. Symptoms include cold skin and a prickling feeling, followed by numbness and inflamed or discolored skin. As frostbite worsens, skin may become hard or waxy-looking.

Exposed skin in cold, windy weather is most vulnerable to frostbite, but it can affect skin covered by gloves or other clothing. You may not realize you have frostbite until someone else points it out.

You can treat frostnip by rewarming. All other frostbite requires medical attention because it can permanently damage skin, muscle, bone and other tissue.

Signs and symptoms of frostbite include:

• At first, cold skin and a prickling feeling
• Numbness
• Skin that looks red, white, bluish-white, grayish-yellow, purplish, brown or ashen, depending on the severity of the condition and usual skin color
• Hard or waxy-looking skin
• Clumsiness due to joint and muscle stiffness
• Blistering after rewarming, in severe cases

Frostbite is most common on the fingers, toes, nose, ears, cheeks and chin. Because of skin numbness, you may not realize you have frostbite until someone points it out. Changes in the color of the affected area might be difficult to see on brown or Black skin.

Frostbite occurs in several stages:

• Frostnip. Frostnip is a mild form of frostbite. Continued cold exposure leads to numbness in the affected area. As your skin warms, you may feel pain and tingling. Frostnip doesn't cause permanent skin damage.
• Superficial frostbite. Superficial frostbite causes slight changes in skin color. The skin may begin to feel warm — a sign of serious skin involvement. If you treat frostbite with rewarming at this stage, the surface of the skin may appear mottled. And you may notice stinging, burning and swelling. A fluid-filled blister may appear 12 to 36 hours after rewarming the skin.
• Deep (severe) frostbite. As frostbite progresses, it affects all layers of the skin as well as the tissues that lie below. The skin turns white or blue-gray and you lose all sensation of cold, pain or discomfort in the area. Joints or muscles may stop working. Large blisters form 24 to 48 hours after rewarming. The tissue turns black and hard as it dies.

When to see a doctor

Seek medical attention for frostbite if you experience:

• Signs and symptoms of superficial or deep frostbite
• Increased pain, swelling, inflammation or discharge in the area that was frostbitten
• Fever
• New, unexplained symptoms

Seek emergency care for hard, cold, blotchy skin.

Also get emergency medical help if you suspect hypothermia, a condition in which the body loses heat faster than it can be produced. Signs and symptoms of hypothermia include:

• Intense shivering
• Slurred speech
• Drowsiness and loss of coordination

Wrap the person with hypothermia in warm blankets until help arrives.

What you can do in the meantime

While you wait for emergency medical help or a doctor's appointment, take appropriate self-care measures, such as:

• Removing wet clothing
• Protecting the affected area from further cold
• Not walking on frostbitten feet
• Reducing pain with a pain reliever

Frostbite occurs when skin and underlying tissues freeze. The most common cause of frostbite is exposure to cold-weather conditions. But it can also be caused by direct contact with ice, freezing metals or very cold liquids.

Specific conditions that lead to frostbite include:

• Wearing clothing that isn't suitable for the conditions you're in — for example, it doesn't protect against cold, windy or wet weather or it's too tight.
• Staying out in the cold and wind too long. Risk increases as air temperature falls below 5 F (minus 15 C), even with low wind speeds. In wind chill of minus 16.6 F (minus 27 C), frostbite can occur on exposed skin in less than 30 minutes.

The following factors increase the risk of frostbite:

• Medical conditions that affect your ability to feel or respond to cold, such as dehydration, excessive sweating, exhaustion, diabetes and poor blood flow in the limbs
• Alcohol or drug use
• Smoking
• Fear, panic or mental illness that impairs your judgment
• Previous frostbite or cold injury
• Being an infant or older adult, both of whom may have a harder time producing and retaining body heat
• Being at high altitude, where there's less oxygen

Complications of frostbite include:

• Increased sensitivity to cold
• Increased risk of developing frostbite again
• Long-term numbness in the affected area
• Excessive sweating (hyperhidrosis)
• Changes in skin color
• Changes in or loss of nails
• Joint stiffness (frostbite arthritis)
• Growth problems in children, if frostbite damages a bone's growth plate
• Infection
• Tetanus
• Gangrene — decay and death of tissue resulting from an interruption of blood flow to the affected area — which can result in amputation
• Hypothermia

Frostbite can be prevented. Here are tips to help you stay safe and warm.

• Limit time outdoors in cold, wet or windy weather. Pay attention to weather forecasts and wind chill readings. In very cold, windy weather, exposed skin can develop frostbite in a matter of minutes.
• Dress in several layers of loose, warm clothing. Air trapped between the layers of clothing acts as insulation against the cold. Wear windproof and waterproof outer garments to protect against wind, snow and rain. Choose undergarments that wick moisture away from the skin. Change out of wet clothing — particularly gloves, hats and socks — as soon as possible.
• Wear a hat or headband that fully covers the ears. Heavy woolen or windproof materials make the best headwear for cold protection.
• Wear mittens rather than gloves. Mittens provide better protection. Or try a thin pair of glove liners made of a wicking material (such as polypropylene) under a pair of heavier gloves or mittens.
• Wear socks and sock liners that fit well, wick moisture and provide insulation. Consider hand and foot warmers as well. Be sure foot warmers don't make boots too tight, restricting blood flow.
• Watch for signs of frostbite. Early signs of frostbite include changes in skin color, prickling and numbness. Seek warm shelter if you notice signs of frostbite.
• Plan to protect yourself. When traveling in cold weather, carry emergency supplies and warm clothing in case you become stranded. If you'll be in remote territory, tell others your route and expected return date.
• Don't drink alcohol if you plan to be outdoors in cold weather. Alcoholic beverages cause the body to lose heat faster.
• Eat well-balanced meals and stay hydrated. Doing this even before you go out in the cold will help you stay warm.
• Keep moving. Exercise can get the blood flowing and help you stay warm, but don't do it to the point of exhaustion.

Diagnosing frostbite is based on your signs and symptoms, skin appearance, and a review of recent activities in which you were exposed to cold.

Your doctor may order X-rays, a bone scan or an MRI to help determine the severity of the frostbite and check for bone or muscle damage.

Mild frostbite (frostnip) can be treated at home with first-aid care. For all other frostbite, after appropriate first aid and assessment for hypothermia, medical treatment may involve rewarming, medications, wound care, surgery and various therapies, depending on the severity of the injury.

• Rewarming of the skin. If the skin hasn't been rewarmed already, your doctor will rewarm the area using a warm-water bath for 15 to 30 minutes. The skin may turn soft. You may be encouraged to gently move the affected area as it rewarms.
• Oral pain medicine. Because the rewarming process can be painful, your doctor will likely give you a drug to ease the pain.
• Protecting the injury. Once the skin thaws, your doctor may loosely wrap the area with sterile sheets, towels or dressings to protect the skin. Or the doctor may protect your fingers or toes as they thaw by gently separating them from each other. And you may need to elevate the affected area to reduce swelling.
• Removal of damaged tissue (debridement). To heal properly, frostbitten skin needs to be free of damaged, dead or infected tissue. To better distinguish between healthy and dead tissue, your doctor may wait 1 to 3 months before removing damaged tissue.
• Whirlpool therapy or physical therapy. Soaking in a whirlpool bath (hydrotherapy) can aid healing by keeping skin clean and naturally removing dead tissue. You may be encouraged to gently move the affected area.
• Infection-fighting drugs. If the skin or blisters appear infected, your doctor may prescribe oral antibiotics.
• Clot-busting drugs. You may receive an intravenous (IV) injection of a drug that helps restore blood flow (thrombolytic), such as tissue plasminogen activator (TPA). Studies of people with severe frostbite show that TPA lowers the risk of amputation. But these drugs can cause serious bleeding and are typically used only in the most serious situations and within 24 hours of exposure.
• Wound care. A variety of wound care techniques may be used, depending on the extent of injury.
• Surgery. People who have experienced severe frostbite may in time need surgery or amputation to remove dead or decaying tissue.
• Hyperbaric oxygen therapy. Hyperbaric oxygen therapy involves breathing pure oxygen in a pressurized room. Some patients show improved symptoms after this therapy. But more study is needed.

To care for your skin after frostbite:

• Take all medications — antibiotics or pain medicine — as prescribed by your doctor. For milder cases of frostbite, a nonprescription pain reliever can help reduce pain and inflammation.
• For superficial frostbite that has been rewarmed, some people find it soothing to apply aloe vera gel or lotion to the affected area several times a day.
• Get out of the cold and wind. Don't thaw or warm the affected area if it might refreeze. Remove wet clothes once you're indoors. Seek emergency medical care.
• Remove rings or other tight items. Try to do this before the affected area swells.
• Don't walk on frostbitten feet, if possible
• Don't apply direct heat or rub the area.
• Don't break blisters that may develop. Blisters act like a bandage. Allow blisters to break on their own.

Call your doctor if you suspect you have frostbite or hypothermia. Depending on the severity of your symptoms, you may be told to go to an emergency room.

If you have time before your appointment, use the information below to get ready for your medical evaluation.

What you can do

• List any signs and symptoms you've been experiencing and for how long. It will help your doctor to have as many details as possible about your cold exposure and to know if your signs and symptoms have changed or progressed.
• List your key medical information, including any other conditions with which you've been diagnosed. Also list all medications you're taking, including nonprescription medications and supplements.
• Make a note of the date of your last tetanus shot. Frostbite increases the risk of tetanus. If you haven't been vaccinated or if your last shot was more than 10 years ago, your doctor may recommend that you be vaccinated.
• List questions to ask your doctor. Being prepared will help you make the most of the time you have with your doctor.

For frostbite, some basic questions to ask your doctor include:

• Are tests needed to confirm the diagnosis?
• What are my treatment options and the pros and cons for each?
• What results can I expect?
• What skin care routines do you recommend while the frostbite heals?
• What kind of follow-up, if any, should I expect?
• What changes in my skin should I look for?

Don't hesitate to ask any other questions that occur to you.