Healthy skin contains melanin, a brown pigment produced from the amino acid tyrosine by pigment cells (melanocytes) in the skin. If skin affected by vitiligo is examined under the microscope, the melanocytes are absent and there are signs of inflammation in the deeper layer of the skin.

It is not known exactly why some people develop this condition and others do not. Some experts believe it is an autoimmune disorder (in which an individual's immune system reacts against part of their own body). In vitiligo, specific autoantibodies against a patient's melanocytes are found in the blood, although it is not known whether autoantibodies are the cause or an effect of the damage seen. There are many autoimmune disorders and some families are more prone to this group of conditions as a whole. Another explanation for vitiligo suggests it is due to a nerve disorder, because nerve damage has been associated with pigment loss in the area of skin served by the nerve.

Vitiligo is equally common in men and women. It can appear at any age but 50 per cent of patients are under 20 when it first appears. Symptoms involve the physical appearance as well as its psychological impact.