Warts are among the most common skin conditions seen in medical practice. They affect approximately 10 % of the general population, with a higher prevalence among children and adolescents, immunocompromised individuals, and those occupationally exposed to shared, humid environments—such as swimming pools, locker rooms, and gyms. Although benign in the vast majority of cases, warts can nevertheless be painful—particularly plantar warts—contagious, unsightly, and a source of social anxiety for those affected. They also tend to multiply and spread if left untreated.
Liquid nitrogen cryotherapy is the gold standard for treating warts—it is recommended by dermatology societies and is the most well-documented treatment option in terms of effectiveness. Each session takes just a few seconds to a few minutes and is available at several of our locations in Quebec with minimal wait time. This guide provides detailed information on how the treatment works, the types of warts it treats, what you’ll experience during and after each session, and the factors that influence the number of sessions needed to achieve complete clearance.
What is a wart, and what causes it?
Warts are benign skin lesions caused by infection of cells in the epidermis—the outermost layer of the skin—by the human papillomavirus, better known by the acronym HPV. This group of viruses includes more than 200 different genotypes, about 20 of which are involved in common skin warts. The genotypes most commonly responsible for skin warts—as distinct from genital warts, which are associated with other genotypes—are primarily HPV-1, HPV-2, HPV-4, and HPV-7. The virus enters the body through small, invisible skin lesions—scratches, cracks, or areas of maceration—and infects basal keratinocytes, causing them to proliferate uncontrollably and form the wart-like lesion.
Transmission occurs through direct contact with a wart—on one’s own skin or on another person’s skin—or through indirect contact with contaminated surfaces in damp environments—such as pool floors and locker rooms. The incubation period is long—ranging from one to twelve months between infection and the appearance of a visible wart. The immune system plays a crucial role in the natural course of warts: in immunocompetent individuals, about two-thirds of warts disappear spontaneously within two years without treatment. However, this natural resolution can take much longer; the lesion may multiply and spread in the meantime, and the unpredictable nature of the course of the disease justifies active treatment in many situations.
The different types of warts and their characteristics
Common warts—verruca vulgaris—are the most common type. They appear as raised keratotic papules with a rough, irregular surface, ranging in color from flesh-colored to grayish, and can measure from a few millimeters to more than one centimeter. They most commonly occur on the fingers, hands, elbows, and knees—areas frequently exposed to minor trauma. Their surface typically shows small black dots corresponding to thrombosed capillaries—a useful clinical sign for distinguishing them from corns and calluses.
Plantar warts—myrmecias or mosaic warts—develop on the sole of the foot. A myrmecia is a solitary, deep plantar wart that is often very painful when pressure is applied because it is pushed inward by weight-bearing—unlike a corn, which is most painful when direct pressure is applied. A mosaic plantar wart is a cluster of multiple small, superficial warts; it is less painful but more widespread and more difficult to treat. Flat warts—verruca plana—are small, slightly raised, smooth lesions that are flesh-colored or slightly pinkish, often found on the face, forehead, backs of the hands, and forearms, particularly in children and adolescents. Filiform warts are thin, elongated, pedunculated lesions, primarily located on the face—around the eyes, nose, and mouth—and on the neck.
How does liquid nitrogen cryotherapy work?
Liquid nitrogen is a cryogenic gas maintained at a temperature of -196 °C. When applied to a wart, it causes rapid and deep freezing of the treated tissue. This sudden drop in temperature leads to the formation of intracellular ice crystals that mechanically destroy cells infected with HPV. Freezing also causes local vasoconstriction followed by vasodilation as the tissue warms, leading to additional vascular damage in the treated area. The local inflammatory reaction triggered by cryotherapy also stimulates the local immune response against the virus—an additional mechanism that contributes to the elimination of HPV-infected keratinocytes beyond mere mechanical destruction.
Liquid nitrogen is applied to the wart either by direct spraying using a cryogun equipped with a probe suited to the size of the lesion, or by direct contact using a soaked cotton swab. The cryogun spraying technique is more precise and allows for optimal control of the freezing time and the diameter of the treated area. The doctor determines the duration of application—ranging from a few seconds to twenty to thirty seconds, depending on the thickness and type of the wart — and observes the appearance of a white freeze halo around the lesion, a clinical sign indicating that the target tissue has reached the desired therapeutic temperature.
How a Session Unfolds and Expected Outcomes
The cryotherapy session requires no special preparation. The doctor or nurse practitioner examines the lesion, confirms the clinical diagnosis of a wart, and applies liquid nitrogen using the appropriate technique. For thick, hyperkeratotic warts, debridement using a curette or a keratolytic emollient may be performed prior to treatment to improve the penetration of the cold. The sensation felt during application is an intense, transient stinging pain—similar to a cold burn—that gradually subsides within minutes after the application is stopped.
In the hours following the session, redness, swelling and sometimes phlyctenes - blisters filled with clear or serum-like fluid - form on the treated area. This reaction is normal and expected - it reflects the local inflammatory response. The phlyctenes should not be intentionally pierced - they will reabsorb naturally within a few days. A protective dressing can be applied. Local sensitivity and sometimes moderate pain persist for two to three days after the session, but are generally well managed with paracetamol. The scab that forms on the treated area will fall off spontaneously within one to two weeks, giving way to new underlying skin. Depending on the response, a new session is scheduled two to four weeks after the previous one.
Frequently asked questions about wart treatment at Clinique Omicron
How many cryotherapy sessions are needed to remove a wart?
The number of sessions varies considerably depending on the size, thickness, and age of the wart, its location—deep plantar warts are among the most stubborn—and the individual’s immune response. On average, two to five sessions spaced two to four weeks apart are needed to achieve complete clearance. Some warts respond after the first or second session, while others may require more. Extensive mosaic warts and periungual warts generally take the longest to treat. Combining cryotherapy with a topical keratolytic treatment—such as salicylic acid applied between sessions—improves remission rates and often reduces the number of sessions required.
Is liquid nitrogen treatment for warts covered by RAMQ?
Cryotherapy for warts performed by a participating physician is covered by the RAMQ when done for medical purposes. The initial medical consultation and treatment sessions are covered upon presentation of the health insurance card. Certain situations—such as the treatment of warts that are purely cosmetic in adults with no symptoms or risk of complications—may be evaluated differently depending on the clinical context. The physician documents the medical indication in the patient’s medical record. For individuals without a family doctor, physicians at Clinique Omicron’s various locations across Quebec can evaluate and treat warts directly during a consultation.
Can warts reappear after cryotherapy?
Yes—recurrences are possible. Cryotherapy destroys the visible wart and the infected keratinocytes in the treated area, but it does not necessarily eliminate all HPV viral particles present in the surrounding skin. If infected cells remain at the edge of the treated area, a new wart may reappear in the same spot or nearby. Furthermore, reinfection is possible if risk factors persist—contact with contaminated surfaces, walking barefoot in shared damp areas, or direct contact with active warts. Hygiene measures—such as not walking barefoot in locker rooms and swimming pools and not sharing pedicure tools—reduce the risk of reinfection after treatment.
Are there alternative treatments to cryotherapy for warts?
There are several options depending on the situation. Salicylic acid-based keratolytic treatments—available over the counter at pharmacies—are effective against shallow, superficial warts, but require strict daily application for several weeks to months. Electrocautery—destruction using an electric current—is an option for warts that are resistant to cryotherapy and is performed under local anesthesia. Cantharidin—a vesicant extracted from an insect—is used by some dermatologists, particularly in children, to avoid the pain associated with cryotherapy. Local immunotherapy—application of diphenylcyclopropenone or intralesional injections of candidine—is reserved for multiple or very resistant warts. Surgical excision is rarely indicated for common warts due to the risk of scarring. The doctor determines the optimal treatment strategy based on the wart’s characteristics and the patient’s preferences.
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