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Nitrogen is a gas found in the air. When it is cooled to -300 º F (-196º C), nitrogen forms a liquid. When liquid nitrogen is applied to a skin lesion, it results in a blister under the wart or keratosis, separating them from the underlying skin. After a few days, the blister peels off, taking the skin lesion with it.
Treatment is typically accompanied by a stinging and burning sensation that occurs while the lesion is being frozen and for a few minutes afterwards, during thawing. A blister will usually form under the skin lesion in 3-24 hours after treatment.
The blister may be filled with a clear fluid or blood. This is a normal response to cryotherapy. Sometimes a blister may not form, and the skin lesion may just shrivel up. The blister will usually crust over and fall off by itself in a few days to weeks.
In the overwhelming number of cases, there is no pain after the treatment (beyond the first few minutes). No special care is required. Bathing and normal activities may be continued.
If the skin lesion is still present once the blister clears, a repeat treatment with liquid nitrogen might be necessary.
Sometimes all that occurs is some inflammation or crusting around the lesion. In others, there may be fairly severe inflammation with a large blister occurring under the lesion. Because Cantharidin is a blistering agent, it is important to let the liquid dry on the lesion. Otherwise, it may be rubbed into the adjacent skin, and cause a blister on the normal skin. If this does occur, it's not harmful.
The advantage of Cantharidin over the other methods of treatments is that it is extremely unusual to have any pain when the medication is applied. However, it is a slower method of treatment, and repeated applications of the liquid may be needed. Some discoloration of the skin can occur after treatment. However, there is no resultant scarring. No special care is required after treatment. The patient may bathe, swim, etc. Should any untoward reaction occur, contact your dermatologist immediately.