Frostbite is an injury where exposure to extreme cold causes the freezing of skin and underlying tissues. This localized freezing damages cells and blood vessels, most commonly affecting extremities like the fingers, toes, nose, and ears. The visual appearance changes dramatically as the injury progresses, making skin color a primary indicator of tissue damage depth. Understanding these color changes is important for recognizing severity and ensuring the proper immediate response.
Appearance of Frostbite by Severity
In the initial, mildest stage, sometimes called frostnip, the affected skin appears red and may feel cold to the touch. This initial redness is followed by pallor as blood vessels constrict to preserve core body temperature, causing the skin to turn white or a pale, grayish-yellow color. The sensation of cold gives way to numbness and tingling, but the skin remains soft and pliable beneath the surface.
As the injury deepens into superficial frostbite, the skin takes on a waxy appearance and feels hard or frozen to the touch. The color is distinctly white or pale blue, indicating that the top layers of the skin have crystallized. Although the skin may feel slightly warm upon first contact due to underlying tissue damage, it is deceptively frozen and should not be confused with rewarming.
The most severe form is deep frostbite, which affects all layers of the skin and underlying soft tissues, including tendons and bone. The frozen tissue feels hard and solid, with a complete loss of sensation. The skin color shifts to a mottled blue, grayish-yellow, or purplish hue, reflecting the cessation of blood flow and tissue death. This deep discoloration is a sign of permanent damage and requires immediate medical attention.
Immediate First Aid Steps
Recognizing frostbite requires moving immediately to a warm, sheltered location to prevent further cold exposure. Gently remove all wet clothing, including socks and gloves, along with any constrictive items like rings or jewelry, before swelling begins. The affected area must not be rubbed with snow or massaged, as this mechanical trauma can cause additional damage to the fragile, frozen tissues.
The most effective field treatment involves rapid rewarming in a water bath heated to a constant temperature between 98.6°F and 102.6°F (37°C and 39°C). The affected part should be soaked for 15 to 30 minutes, or until the skin becomes soft and pliable, indicating thawing. Rewarming should only be attempted if there is no risk of the tissue refreezing before reaching a medical facility, as a thaw-refreeze cycle significantly worsens the injury.
Direct dry heat sources, such as a fireplace, stove, or heating pad, should be avoided because the affected area is numb and a burn could occur without the person realizing it. While rewarming, the patient may experience significant pain, and a nonprescription pain reliever can be taken. If the feet or legs are affected, the patient should avoid walking on the frozen tissue to minimize further injury.
What Happens After Tissue Thaws
Once the frozen tissue has thawed, a complex and often painful inflammatory response begins. Within a few hours, the affected area will become significantly swollen (edema), which may last for several days. Blisters typically form within 12 to 36 hours after rewarming, and their content indicates the injury’s depth.
Superficial injuries tend to produce large, clear or milky fluid-filled blisters, suggesting the underlying tissue may survive. In contrast, deep tissue damage results in smaller, dark, or hemorrhagic blisters filled with blood, signaling severe injury to deeper blood vessels. These blisters should not be broken, as the fluid inside provides a sterile environment that protects the underlying skin.
Over the next one to two weeks, the damaged skin will contract and dry out, eventually forming a thick, dark, hard scab called an eschar. If the injury was superficial, new pink skin may appear beneath the eschar as it sloughs off. For deep frostbite, the eschar will be thick and gangrenous, and the tissue underneath may be permanently nonviable, sometimes leading to the natural separation of the damaged part. Long-term effects can include chronic cold sensitivity, persistent numbness, and excessive sweating due to nerve damage.