Cryotherapy refers to a treatment in which surface skin lesions are frozen.Cryogens used to freeze skin lesions include:
- Liquid nitrogen (the most common method used by doctors)
- Carbon dioxide snow (more commonly used 20 years ago)
- Dimethyl ether and propane or DMEP (available over the counter as Wartner®)
Carbon dioxide snow
Carbon dioxide cryotherapy involves making a cylinder of frozen carbon dioxide snow (–78.5°C) or a slush combined with acetone. It is applied directly to the skin lesion.
DMEP works at a temperature of –57°C. It comes in an aerosol can available over the counter. It is used to treat warts using a foam applicator pushed onto the skin lesion for between 10 and 40 seconds, depending on its size and site.
Cryotherapy using liquid nitrogen (temperature –196°C) involves the use of a cryospray, cryoprobe or a cotton-tipped applicator. The nitrogen is applied to the skin lesion for a few seconds, depending on the desired diameter and depth of freeze. The treatment is repeated in some cases, once thawing has completed. This is known as a ‘double freeze-thaw’.
Cryotherapy stings and may be painful, at the time and for a variable period afterwards. There may be immediate swelling and redness. This may be reduced by applying a topical steroid on a single occasion straight after freezing. Aspirin orally may also reduce the inflammation and discomfort.
Looking after the treatment area
The treated area is likely to blister within a few hours. Sometimes the blister is clear and sometimes it is red or purple because of bleeding (this is harmless). Treatment near the eye may result in a puffy eyelid, especially the following morning, but the swelling settles within a few days. Within a few days a scab forms and the blister gradually dries up.
Usually no special attention is needed during the healing phase. The treated area may be gently washed once or twice daily, and should be kept clean. A dressing is optional, but is advisable if the affected area is subject to trauma or clothes rub on it.
When the blister dries to a scab, apply petroleum jelly (Vaseline) and avoid picking at it. The scab peels off after 5–10 days on the face and 3 weeks on the hand. A sore or scab may persist as long as 3 months on the lower leg because healing in this site is often slow.
Delayed effects of cryotherapy
Clear and haemorrhagic blisters
Results of cryotherapy
After a standard freeze of a actinic keratosis, seborrhoeic keratosis or viral wart, the skin may appear entirely normal without any sign of the original skin lesion.
Complications of cryotherapy
The main concern is secondary wound infection, but this is uncommon. Infection may cause increased pain, swelling, thick yellow blister fluid, a purulent discharge and/or redness around the treated area. Consult your doctor if you are concerned: topical antiseptics and/or oral antibiotics may be necessary.
Other undesirable effects may include:
- Delayed healing and ulceration
- Local nerve damage (usually temporary)
- Permanenthypopigmentation or scar
- Persistent or recurrent skin lesions, necessitating further cryotherapy, surgery or other treatment.