Liquid nitrogen is a cryogenic substance used in medicine for a targeted procedure called cryotherapy or cryosurgery. It maintains an extremely low temperature of approximately -196°C (-321°F). Cryotherapy is commonly employed to destroy unwanted tissue, such as benign lesions (warts, skin tags) and precancerous lesions (actinic keratoses). Since the goal is controlled tissue destruction, the process initiates a wound healing response, meaning a permanent mark or scar is a possible outcome.
The Mechanism of Cold Injury to Skin
Cryotherapy works by rapidly freezing the targeted skin cells to eliminate the lesion. The mechanism of cell death occurs in two phases: physical destruction and vascular damage. During the physical phase, the rapid temperature drop causes water within the cells to form sharp ice crystals.
This crystallization directly punctures cell membranes and draws water out of the cells, resulting in severe dehydration and electrolyte imbalances. This process destroys the cell structure, leading to necrosis. The subsequent thaw phase causes further cell injury due to osmotic shock as water rushes back into the compromised cells.
The second phase involves the microcirculation. The extreme cold damages the small blood vessels supplying the area, leading to blood clotting and stasis. This cuts off oxygen and nutrients to the treated tissue, resulting in ischemic necrosis. The destruction of the lesion then begins the body’s natural wound healing cascade, which can sometimes result in a visible mark.
Factors That Influence The Final Outcome
The probability of a permanent mark depends heavily on the specifics of the procedure, particularly the duration and depth of the freeze. Superficial treatments, often used for thin or small lesions, involve brief applications and generally lead to less substantial tissue damage, minimizing the risk of true scarring. Conversely, deeper or longer freezes, required for thicker lesions, penetrate further into the dermis, increasing the likelihood of a noticeable mark.
The location of the treatment area also plays a role because skin tension and blood flow vary across the body. Areas with higher skin tension or poor circulation, such as the back, shoulders, or joints, can be more prone to developing hypertrophic or keloid scars. Smaller, thinner lesions generally have a better treatment outcome and lower chance of permanent marking.
A pigment change is the most common long-term side effect of cryotherapy, distinct from a true scar. Liquid nitrogen often destroys melanocytes, the cells responsible for producing skin pigment, which are highly sensitive to cold temperatures. This damage results in hypopigmentation, creating a white or light-colored patch of skin at the treatment site. This color change is more likely to be permanent in individuals with darker skin tones.
Wound Care and Techniques to Minimize Marks
Clinicians use specific application methods to help control the freeze and minimize damage to surrounding healthy tissue. Techniques like spray application or using a cotton-tipped applicator allow for precise targeting, which helps to maintain a defined margin around the lesion. The rate of the thaw cycle is also a factor, as a rapid thaw can sometimes be preferred for benign lesions in areas prone to scarring because it helps limit the extent of tissue damage.
Post-procedure care helps manage the final appearance of the treated area. A blister, which can be clear or blood-filled, often forms within hours, indicating that the treatment was effective. Patients should avoid puncturing this blister, as the intact skin roof acts as a natural, sterile dressing that protects the developing new tissue underneath.
If the blister breaks or the area scabs, the goal is to promote moist wound healing to encourage skin regeneration. Gently cleaning the area daily with fragrance-free soap and water is recommended, followed by the application of a moisturizing ointment, such as petroleum jelly, for up to two weeks. This helps prevent the formation of a dry scab, which can impede the healing process and contribute to scar tissue development. Protecting the healing skin from sun exposure with clothing or a broad-spectrum sunscreen is necessary to prevent discoloration and reduce the chance of a noticeable mark.