Keratinocytes need to be frozen to -50 C for optimum destruction. Melanocytes are more delicate and only require -5 C for destruction. This is the reason for the resulting hypopigmentation following cryotherapy on darker-skinned individuals. The last response to cryotherapy is inflammation. This usually is observed as erythema and edema.
Inflammation is the response to cell death and helps in local cell destruction.
A thorough cryotherapy treatment will cause basement membrane separation, which may result in blister formation. They include the spray freeze technique, applicator technique and the thermo-coupler method. Liquid nitrogen is the best and universal freezing source because of its low boiling point and ease of use. Other sources of freezing, such as Freon, carbon dioxide, and nitrous oxide, do exist but are not as efficient in destroying lesions due to their higher boiling points. Prior to freezing the lesion, the patient needs to be informed of the procedure and verbal or written consent obtained.