When a dermatologist sprays or dabs liquid nitrogen on a growth, the cold kills the cells of the growth, and the skin then sheds the dead tissue and rebuilds itself. Liquid nitrogen is the coldest substance in routine office use, which is why one tool can treat warts, sun spots and some small skin cancers.1Journal of the American Academy of Dermatology. What Happens When the Dermatologist Freezes Skin? Much of the damage happens as the skin thaws and in the days after, not in the few seconds of freezing, so the spot looks worse before it looks better.
What the Cold Does Inside the Cells
Under a microscope, frozen skin shows ice crystals forming inside the cells themselves.2PubMed Central. Mechanisms of tissue destruction following cryosurgery When cooling is very fast, the water inside a cell freezes before it can escape, and that ice tears the cell’s outer membrane.3Brymill. What Happens When the Dermatologist Freezes Skin?
That is why doctors often use a freeze-thaw cycle: freeze the spot, let it thaw fully, then repeat. Each thaw adds its own damage, so a second cycle kills more cells than one long freeze would. If your doctor waits between sprays, that pause is part of the treatment, not hesitation.
Depth matters too. Cold reaches deeper the longer and colder the freeze, and a white frozen ring spreading around the spot shows how far the ice has traveled. A thick growth needs a frozen zone that extends below and beyond what you can see, so a quick dab won’t do.
Doctors typically freeze a small rim of normal-looking skin so the base of the growth is treated too. Because that rim is frozen on purpose, you may notice redness or a blister slightly beyond the growth’s edge afterward. That is expected, not a mistake.
Thawing and loss of blood flow finish the job. Slow thawing adds to the destruction through water shifts and damage to small blood vessels.4Brymill. What Happens When the Dermatologist Freezes Skin? Cooling also makes the skin’s blood vessels clamp down, and they stay narrowed even after the skin warms back up.5PubMed Central. Cryotherapy-Induced Persistent Vasoconstriction After Cutaneous Cooling: Hysteresis Between Skin Temperature and Blood Perfusion The treated spot is starved of blood for a while after the visit, which helps finish off cells that survived the freeze. This loss of blood supply comes after the direct cell damage rather than causing it.6PubMed Central. Mechanisms of tissue destruction following cryosurgery
Your body’s defenses may join in afterward. Dying cells release pieces of virus or abnormal cells that can alert the immune system, which may help fight a wart virus or a tumor.7PubMed Central. Structural and Immunological Effects of Skin Cryoablation in a Mouse Model This immune boost is still being studied, and you can’t count on it to clear growths elsewhere on your body.
What You’ll Feel and See Over the Next Few Weeks
During the spray the spot turns white and stings or burns for a minute or two. Within hours it becomes red and puffy, and sometimes throbs. A blister, sometimes filled with clear or bloody fluid, may form within a day. The blister dries into a scab that usually falls off in one to three weeks, longer on the legs. Fresh pink skin underneath slowly settles toward your normal color.
The pain comes from inflammation, not only from the cold.8PubMed. Different inflammatory mediators induce inflammation and pain after application of liquid nitrogen to the skin The damaged tissue releases chemical signals that make the area sore and tender to touch for a while.9PubMed. Different inflammatory mediators induce inflammation and pain after application of liquid nitrogen to the skin An anti-inflammatory pain reliever such as ibuprofen may ease the soreness, if it is safe for you to take.
Soreness usually fades over a few days as the inflammation settles. A spot on a fingertip or the sole of the foot can stay tender longer because those areas take pressure. Pain that is getting steadily worse after several days, rather than gradually easing, is worth mentioning to the clinic, since normal healing should trend better.
A blister forms because fluid leaks into the space between damaged skin layers, so it shows the treatment reached the tissue it was meant to. Not everyone blisters, and a spot that stays red and then scabs without one can still have been treated well. Blood-tinged fluid is common after freezing and does not by itself mean something went wrong.
At home, wash the spot gently and keep it clean. A plain bandage helps if it rubs on clothing. Leave a blister alone; if it is large and painful, ask the clinic about draining it. Don’t pick the scab, since removing it early raises the chance of a mark.
Normal healing means redness, swelling and tenderness that peak in the first day or two and then shrink. Spreading redness, increasing warmth, yellow pus or fever are reasons to call your doctor. A crust that looks dark or yellowish-brown is usually just dried fluid and dead tissue, which is different from thick pus with a bad smell or a growing painful area.
Healing usually leaves little scarring because the skin’s framework survives. Freezing tends to spare the tough fibers that give skin its structure, so new skin can rebuild along the intact framework.10PubMed Central. Wound healing and scarring after cryosurgery
How Well It Works for Warts
Freezing clears about 75% of common warts overall.11PostÄ™py Dermatologii i Alergologii. Clinical practice trends in cryosurgery: a retrospective study of cutaneous lesions Older warts, having many warts, and fewer treatments all lower the odds.12PostÄ™py Dermatologii i Alergologii. Clinical practice trends in cryosurgery: a retrospective study of cutaneous lesions Weekly sessions clear warts faster, but the overall cure depends on how many sessions you get.13PubMed Central. Cryosurgery for common skin lesions. Treatment in family physicians’ offices For warts on the sole of the foot, filing down the thick skin first and using two freeze-thaw cycles works better.14PubMed Central. Cryosurgery for common skin lesions. Treatment in family physicians’ offices
One session often isn’t enough because the wart virus can sit deeper than a single freeze reaches. A wart that shrinks but doesn’t vanish usually needs another round in two to four weeks. Stopping after one session is a common reason warts seem to come back, so ask your doctor how many sessions to plan for before giving up.
Over-the-counter salicylic acid between sessions is often suggested alongside freezing. Avoid picking at warts, which can spread the virus to nearby skin.
After treatment the wart often turns dark or blackish as its tiny blood vessels clot. This dark look usually means the tissue is dying rather than that something is wrong. Once the dead layer sheds, you may see normal skin lines crossing the area again. Warts interrupt those lines, so their return is one good sign the wart is gone, along with a flat pink area with no raised rough surface.
How Well It Works for Sun Spots and Other Growths
Actinic keratoses, rough scaly sun spots that can sometimes turn into skin cancer, are one of the most common reasons to freeze skin.15Postępy Dermatologii i Alergologii. Clinical practice trends in cryosurgery: a retrospective study of cutaneous lesions Freezing clears between 75% and 99% of sun spots.16Postępy Dermatologii i Alergologii. Clinical practice trends in cryosurgery: a retrospective study of cutaneous lesions How long and how cold the spot is frozen matters, with cure rates from 39% to 83% depending on the method.17PubMed Central. Cryotherapy for Actinic Keratosis: Basic Principles and Literature Review When the skin surface was reliably brought to -5°C, nearly all sun spots were cleared at six weeks.18PubMed Central. Cryotherapy for Actinic Keratosis: Basic Principles and Literature Review
A treated sun spot typically reddens, may blister, then crusts over and flakes away, leaving pink skin that gradually evens out over several weeks. If the roughness or scaliness is still there after the skin has healed, the spot may need a second treatment, and that is a common reason for a follow-up. A sun spot that comes back in the same place, or one that becomes thick, tender, bleeds, or grows quickly, should be rechecked rather than simply frozen again. Those changes can suggest the growth has progressed to skin cancer, and a biopsy may then be more appropriate than another freeze.
Pairing freezing with a cream works better than freezing alone. Freezing plus a prescription skin cream cleared all spots in about 1.7 times as many people as one treatment alone.19PubMed. Cryosurgery combined with topical interventions for actinic keratosis: a systematic review and meta-analysis Fluorouracil cream combined with freezing is a proven but underused option.20PubMed. Practice trends in the treatment of actinic keratosis in the United States: 0.5% fluorouracil and combination cryotherapy plus fluorouracil are underused despite evidence of benefit If you have many sun spots, ask whether a cream should go with the freezing.
Other growths can be frozen too. Freezing also works for seborrheic keratoses, molluscum, dermatofibromas, keloids and some harmless moles.21PubMed Central. Cryosurgery for common skin lesions. Treatment in family physicians’ offices Small basal cell skin cancers frozen to -50°C to -60°C showed no cancer left when the spots were later cut out and examined.22PubMed. Histologic cure of basal cell carcinoma treated with cryosurgery A simple cotton-swab dab, though, can’t kill cells deeper than about 1.5 mm, too shallow for thick tumors.23ASME International Mechanical Engineering Congress and Exposition. Numerical Modeling of the Tissue Freeze-Thaw Cycle during Cutaneous Cryosurgery using Liquid Nitrogen Spray
A cotton swab dipped in liquid nitrogen suits small, thin, harmless spots. A spray gun reaches colder and deeper and is used for thicker growths. For cancers, doctors may freeze longer or measure the temperature under the skin.
Sometimes a doctor will want a sample first. Freezing destroys the tissue, so nothing is left to examine under a microscope. A spot that looks unusual, bleeds, or grows fast may need a biopsy instead. Ask whether the diagnosis is certain before agreeing to freeze a suspicious spot.
Lighter Patches, Scars and Numbness
Color changes are the most common lasting effect. After a standard freeze, every treated spot developed a lighter patch with a darker ring around it.24PubMed. Pigment changes in human skin after cryotherapy These changes lasted at least six months.25PubMed. Pigment changes in human skin after cryotherapy Pigment cells are especially sensitive to cold and are lost at about -7.5°C with long enough exposure.26PubMed. Selective Cryolysis of Melanocytes: Critical Temperature and Exposure Time to Induce Selective Pigmentary Loss in Yucatan Pig Skin Even brief freezes can leave a light patch while the pigment cells are still there but not passing on color.27PubMed. Pigment changes in human skin after cryotherapy
The treated area may first look pink or red, then lighten over weeks, so the early look is not necessarily the final result. The darker ring around a lighter center can look like a target, and it too tends to fade.
Some brown spots come back darker instead. Skin that was inflamed can react by making extra pigment, so a treated spot may look darker for a while. The result depends on how many pigment cells were destroyed versus how many were only irritated, which is hard to predict beforehand.
Darker skin needs extra thought, because a white patch shows up far more on brown or black skin than on pale skin. Ask about a gentler freeze or a different treatment for spots on your face. Sun protection on the healing spot can help limit darkening at the edges.
Scarring rises with how severe the freeze is. Very deep, severe freezing caused obvious scars, while milder freezing left skin thinner over the long term.28PubMed. Wound healing and scarring after cryosurgery Long-term problems can include slow healing, a dent in the skin, thickened skin, and the growth coming back.29PubMed. Complications of cutaneous cryosurgery
Numbness usually goes away but can be slow. Feeling in the treated skin was reduced at first after every length of freeze.30PubMed Central. Long term effects of cryosurgery on cutaneous sensation. It came back fully, though this took up to 10 months after a 10-second freeze and up to 18 months after longer freezes.31PubMed Central. Long term effects of cryosurgery on cutaneous sensation. In rare cases, freezing a wart over a nerve at the elbow damaged the nerve and caused lasting weakness and numbness.32PubMed. Ulnar neuropathy after liquid nitrogen cryotherapy
Who Shouldn’t Have Their Skin Frozen
Doctors avoid or think twice about freezing in people whose bodies react badly to cold, and in a few other situations:33Indian Journal of Dermatology, Venereology and Leprology. Guidelines for cryotherapy
- Raynaud’s disease, where fingers and toes go white or blue in the cold
- Cold urticaria, hives triggered by cold
- Cryoglobulinemia, blood proteins that clump in the cold
- General cold intolerance
- Unexplained blood disorders
- Spots in areas with poor circulation
- Spots that need a tissue sample for diagnosis
- Recurrent or aggressive skin cancers in high-risk spots such as the temple or the folds beside the nose
In conditions like Raynaud’s or cold urticaria, the body’s reaction to chilling is exaggerated, so freezing can cause far more damage, pain or hives. In cryoglobulinemia, proteins that clump in cold can block small vessels.
Poor circulation changes the risk in a different way. Skin with weak blood flow heals slowly, so a freeze can leave a wound that stays open or becomes infected, especially on the lower legs or feet. People with diabetes or vein or artery disease are more likely to have this problem, so the decision depends on the spot and how well blood reaches it.
Before treatment, mention any history of fingers turning white in the cold or hives from cold. Mention diabetes or poor circulation if the spot is on your lower legs or feet. Say so if a growth is over the elbow or another place where a nerve sits near the surface. And mention it if you scar easily or have had keloids.
Why Liquid Nitrogen Is the Tool of Choice
Liquid nitrogen reaches about -196°C, far colder than older options such as carbon dioxide snow.34Journal of the American Academy of Dermatology. What Happens When the Dermatologist Freezes Skin? That lets it freeze both harmless growths and some skin cancers.35Journal of the American Academy of Dermatology. What Happens When the Dermatologist Freezes Skin? Spray devices let it reach lower temperatures in the skin than a swab.36Journal of the American Academy of Dermatology. What Happens When the Dermatologist Freezes Skin?
Drugstore wart freezers use other chemicals that don’t get as cold. They suit small, simple warts on hands, not the face or suspected sun spots, and a doctor should look at any spot you aren’t sure is a wart.