White patches on skin are a characteristic symptom of vitiligo, a skin disorder that causes the destruction and/or malfunction of the pigment-producing cells. Often these patches are present on the body parts that are most exposed to the sun, such as the arms, hands, legs, feet and face. White patches can also occur at the navel, armpits and genital region. In addition, persons with vitiligo typically exhibit early greying of the hair. It is estimated that 1% of the USA's population have vitiligo, and in total around 100 million people worldwide suffer from this condition.
It is still not known for sure what causes vitiligo. The main theory is that vitiligo is an autoimmune disease, which results in the body's immune system attacking the melanocytes (pigment-producing cells). In fact, people with another autoimmune disease such as hyperthyroidism and adrenocortical insufficiency are more likely to suffer from vitiligo. Some researchers also believe that events such as severe sunburn, certain medications, and emotional stress can trigger vitiligo. In addition, there appears to be a genetic component as well.