Freezing at an extremely low temperature destroys cells. The damage is similar to burning.
To freeze the cells, we use liquid nitrogen (about -196°). The nitrogen is applied either by spraying with a special gun, or dabbing with cotton wool.
This process causes water in the cells to freeze and expand, breaking the cell wall and destroying the cell. This effect applies to both normal and abnormal cells in the treated area. It leads to to redness and sometimes blisters and sores.
When the sore heals, the original skin lesion is no longer present; the aim of cryotherapy is for it to be replaced by new healthy and normal skin cells.
Cryotherapy treats only individual spots. It cannot repair large areas of sun damaged skin. This means that the treated area may still be likely to develop further sun-related problems in future.