Also known as 'cryotherapy', 'cryosurgery' or 'dry ice therapy', this very commonly used non-surgical procedure is for the treatment of a range of skin conditions such as sunspots (solar keratosis), superficial basal cell carcinoma, viral warts, seborrhoeic keratosis, solar lentigo and Bowens disease (also known as squamous cell carcinoma in situ).
The procedure involves using liquid nitrogen to freeze the affected skin. It works by destroying the abnormal skin cells (and a small number of the healthy cells surrounding the abnormal cells) - when these cells return to room temperature they rupture and die. The resulting redness or blistering of the area heals after about two weeks leaving healthy skin once any scab has fallen off.
A complication to be aware of is something called 'hypopigmentation' where the natural pigment of the skin can be paler than normal after treatment. This is due to the destruction of melanocytes - the cells that produce pigment in the skin. This is more noticeable in people with darker skin, but does not always occur and is often temporary if it does.
The liquid nitrogen (which is at a temperature of around -196C) is either sprayed on to the affected area using a type of spray gun, or dabbed on using cotton wool. A short 2-5 second burst with the spray gun is all that is needed to remove most sunspots, while other conditions such as Bowens disease require a slightly longer exposure of 5-10 seconds or a series of spray treatments.
The treatment can be a little painful, with an initial cold sharp stinging pain followed by a much less intense pain which sometimes lasts for a few hours.
Cryotherapy has a 95-98% effectiveness for basal cell carcinoma and an 80-99% effectiveness in treating sunspots.
Cryotherapy is not suitable for certain conditions, for example it is generally not used on the face or the head, partially for cosmetic reasons and partially due to a slightly lower success rate for conditions in these areas. It is also not a suitable treatment for pigmented skin lesions (eg moles) as these should be removed for pathology testing.
It's also important to note that sunspots are continually forming and that cryotherapy only removes existing sunspots - they may - and will return if the skin continues to be exposed to the sun.