Vitiligo is a chronic skin condition characterized by portions of the skin losing their pigment. It occurs when skin pigment cells die or are unable to function. Aside from cases of contact with certain chemicals, the cause of vitiligo is unknown. Research suggests vitiligo may arise from autoimmune, genetic, oxidative stress, neural, or viral causes. Vitiligo is typically classified into two main categories: segmental and non-segmental vitiligo. The global incidence of vitiligo is less than 1%, with some populations averaging 2–3% and rarely as high as 16%. Autoimmune diseases such as Addison's disease, Hashimoto's thyroiditis, and type 1 diabetes mellitus tend to occur more often in people who have vitiligo. There is no cure for vitiligo but many treatment options are available including topical steroids, calcineurin inhibitors, and phototherapy.