Pigment changes in human skin after cryotherapy.

We have investigated the changes in pigmentation and melanocyte distribution in human skin after a standardized freeze injury. All lesions developed hypopigmentation with a peripheral rim of hyperpigmentation. Abnormalities in pigmentation persisted for at least 6 months. Hyperpigmentation was predominantly an epidermal phenomenon. After brief freezes, hypopigmentation persisted despite the presence of functional melanocytes. After prolonged freezes, the consistent finding was an absence of melanosomes in keratinocytes, although melanocytes were present. We conclude that prolonged changes in skin color are frequent after brief freezes and that hypopigmentation is not synonymous with an absence of melanocytes. This suggests that hypopigmentation after the cryosurgical treatment of malignant melanocytic tumors may not equate with cure.