The term cryotherapy means treatment using low temperature and refers to the removal of skin lesions by freezing. The most common substance used by doctors for this purpose is liquid nitrogen.
A wide variety of superficial benign lesions can be treated with cryotherapy. It is most commonly used to remove actinic keratosis (areas of sun-damaged skin predominately on sun-exposed parts of the body), viral warts, seborrhoeic keratosis and other benign lesions.
Cryotherapy is usually well tolerated, but can sometimes be painful if a deep freeze has been necessary. Taking pain relief an hour or so before treatment can reduce discomfort.
Swelling and redness is a normal immediate response to freezing the skin, and usually settles after two to three days. For a short while the treated area may ooze a little and is likely to blister within a few hours. Sometimes the blister is clear and sometimes it is red or purple because of harmless bleeding. 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.
After a standard freeze for a solar keratosis, seborrhoeic keratosis or viral wart, the skin may appear entirely normal without any sign of the original skin lesion.
However, cryotherapy may result in a white mark (hypopigmentation) or a scar, particularly when freezing has been deep or prolonged, as is required for a cancerous lesion. The white mark may be quite noticeable, especially in those with darker complexions. In darker complexions, cryotherapy may also result in a darker mark (hyperpigmentation), especially in sun-exposed areas. Although the appearance often improves with time, the colour change may be permanent.
A hard freeze to the skin over a skin nerve, such as treatment to a viral wart on the side of the finger, can cause numbness of the skin that the nerve supplies. The feeling nearly always returns within a few weeks or months.