This is the use of a cryogen, usually liquid nitrogen (-196 degrees Celsius) to freeze tumour cells. It is most commonly used for treatment of Actinic Keratoses, especially effective when a limited number of lesions exist. No cutting or anesthesia is required. Liquid nitrogen is applied to the growths with a spray device or cotton-tipped applicator to freeze them. They subsequently swell or blister up (like a frost bite), then forms a dry crust and falls off after 1-3 weeks depending on the area treated. The treated area can sometimes be left with an increase in pigmentation (usually in the darker skinned individuals) or a decrease in pigmentation (usually in the lighter skin individuals).