Liquid nitrogen is extremely cold — about −320°F. When it hits the skin, ice crystals form inside the cells of the growth and tear them apart from the inside. The tiny blood vessels feeding the area freeze shut at the same time, so the treated tissue loses its blood supply as well. Those cells die. Over the following days your body lifts the dead layer away, usually by forming a blister underneath it, and new skin grows in from the edges and from the base.
How deep the freeze goes is decided by how long the nitrogen is applied and how much of a margin is taken around the growth. A few seconds treats a thin sun spot. Ten to twenty seconds, sometimes repeated after the skin thaws, is needed for a thick wart. This is the whole skill of the procedure, because the cells that make pigment are among the most cold-sensitive cells in the skin. They die at a shallower freeze than the growth does. That is why a treated spot so often heals a shade or two lighter than the skin around it.
With warts there is a second effect. The freezing kills wart-infected skin, but it also stirs up inflammation, and that inflammation helps your immune system finally notice the virus it has been ignoring. That is part of why repeated sessions work better than one long one.
There is very little to do, which is one of the reasons this procedure is so widely used.
Do not put anything on the spot that morning — no creams, no makeup over it.
If you are treating a thick wart or a callus on the foot, soaking it and filing the surface down with a pumice or emery board for a few days beforehand genuinely helps. The nitrogen has to reach live tissue, and dead callus insulates the wart.
Tell your provider if you take a blood thinner. It does not stop the procedure, but a blood blister is more likely.
Tell your provider if you have had a pale mark from freezing before, or if you are worried about one. This is the conversation to have before, not after.
Eat something. Some people feel faint during minor procedures, and an empty stomach makes it more likely.
You do not need to stop any medication, arrange a driver, or take the day off.
Most of the fear around cryotherapy is out of proportion to what actually happens. Here is the whole thing.
You sit or lie down. The spot is looked at, sometimes with a handheld magnifier, and often marked. There is no injection and no numbing for standard cryotherapy — the freeze itself is the anaesthetic, because cold numbs the nerve endings within a few seconds. Numbing cream is sometimes used for children or for a long list of spots, but it needs about 30 minutes to work, so it has to be planned.
The provider aims the spray or presses the cotton tip against the spot. You will hear a short hiss. A white frost spreads across the spot and a few millimetres around it — that white ring is the point of the exercise, and the provider is watching how far it spreads to judge the depth.
The cold registers a second or two later. Most people describe it as a sharp sting or a burning cold, like touching very cold metal. It builds while the nitrogen is on and it is genuinely uncomfortable, but the freeze itself lasts five to twenty seconds. Then it stops.
Thawing is the part people are not warned about, and it stings more than the freeze for many people. The skin turns from white back to red over about 30 to 60 seconds, and there is a deep, aching, throbbing burn as it does. It fades over a minute or two. If a second freeze is planned, it happens after the skin has fully thawed, and the second one hurts more than the first because the nerves are already irritated.
The spot goes red and starts to swell within minutes. It may look worse than you expected. Nothing is put on it in most cases, or a small dressing if it is somewhere that rubs.
The freeze is seconds. A single spot is over in under a minute, and the whole appointment is usually 5 to 15 minutes including the conversation. A list of ten actinic keratoses might take 15 to 20 minutes.
Yes. There is no sedation, no injection and nothing that affects you. People go straight back to work. The one exception is a spot on the sole of the foot, which can be sore enough to make walking uncomfortable for a day or two.
This is the normal course. It looks alarming and it is meant to.
Red, swollen, and stinging or throbbing. Plain paracetamol or ibuprofen handles it. A cool compress helps. The area around the spot may swell more than the spot itself — eyelids and lips in particular can puff up noticeably.
A blister usually forms. It may be clear or filled with blood, which looks dramatic and purple-black and is not a complication. A blood blister after freezing is expected, especially on the hands and fingers. Leave it alone. Do not pop it — intact blister skin is the best dressing there is. If it bursts on its own, wash it with soap and water, apply plain petroleum jelly, and cover it with a plaster.
The blister flattens and dries into a crust or scab. It is often darker than the surrounding skin. Keep it moist with petroleum jelly rather than letting it dry hard — moist wounds heal faster and with less scarring than dry ones. Antibiotic ointment is not needed and causes an allergic rash in a fair number of people.
The crust lifts off on its own, taking the growth with it. The skin underneath is pink and slightly shiny. Do not pick it off early — pulling a crust off before the skin under it is ready is the main cause of a scar from a procedure that does not usually scar.
The pink fades over one to three months. What is left in its place is the part that matters: the spot is often lighter than the skin around it. On light skin this usually blends back over months. On brown and Black skin it may not fully blend back at all.
You can shower normally from day one. Avoid soaking the area in a bath, pool or hot tub until the crust has come off. Sunscreen on the healing spot for the next few months genuinely reduces how noticeable the final mark is.
How soon: the growth lifts off with the crust over one to three weeks. You do not see the final result until the pinkness settles, which takes another one to three months.
Sun spots, seborrheic keratoses and skin tags: usually one session clears them. Thick ones sometimes need a second.
Actinic keratoses: one freeze clears most individual patches. Clearance rates in studies sit around 70 to 80 percent per lesion. Freezing only treats what can be seen, so if you have widespread sun damage a cream or photodynamic therapy that treats a whole field is often used alongside it.
Warts: this is where expectations go wrong. One session very rarely cures a wart. It usually takes three to six sessions two to three weeks apart, and even then the results are mixed — head-to-head trials put cryotherapy at broadly similar cure rates to diligent daily salicylic acid at home. If you have had three or four sessions with no change, that is a reason to change plan, not to keep going.
Molluscum: two or three visits, each freezing the bumps present that day. New ones keep appearing until the immune system clears the virus, so it is a holding action rather than a cure.
Keloids: freezing softens and shrinks small keloids, and it is usually done to make them easier to inject rather than as a treatment on its own.
How long results last: once a growth is gone it is gone. But cryotherapy does not stop new ones forming. Sun spots, seborrheic keratoses and actinic keratoses come from accumulated sun exposure, so new ones will keep appearing. Warts can recur because the virus is still in the surrounding skin.
There are over-the-counter freezing kits — canisters with a foam applicator, sold for warts. They are not the same thing and it is worth knowing why.
Clinic liquid nitrogen is about −320°F. The home kits use a compressed gas mixture that reaches roughly −70°F to −110°F at the applicator, and much less than that by the time it reaches the base of a wart. They are meaningfully weaker. For a small, thin wart on a hand they sometimes work, particularly if you file the surface first and repeat as directed. For a thick wart, a wart on the sole, or anything on the face, they usually do not.
They also carry the same pigment risk as clinic freezing, without anyone judging the depth. Home kits have caused blisters, ulcers and permanent pale marks, and they should not be used on the face, on genitals, on children under four, or by anyone with diabetes or poor circulation.
For a wart, daily salicylic acid at home is the better-evidenced self-treatment. It is slow and boring — six to twelve weeks of filing and applying — but it holds up well in trials against freezing, and it will not leave a pale spot.
One thing to be direct about. Cutting, burning, tying off with thread or dental floss, or applying caustic paste to a growth at home is how people end up in clinic with an infection, a bad scar, or a wound that will not heal. The serious version of the problem is quieter: some of what people remove at home is not what they think it is. A basal cell carcinoma, an early melanoma and a harmless keratosis can look similar, and destroying one at home means nobody ever looks at it. If a growth is changing, bleeding, growing or new, it needs a diagnosis before it needs a treatment.