What are the causes of vitiligo, and how does it go away?

Skin pigmentation. An auto-immune, inflammatory condition of the skin in which the body attacks the cells that mix the pigment of the skin. Treatment varies on the condition's progress. I usually apply the 1/3 rule: 1/3 of patients respond very well to treatment and the condition disappears; 1/3 of patients are stable after treatment; and 1/3 of patients progress instead of responding to treatment. Cause is unknown.
Autoimmune disorder. Vitiligo is and autoimmune disorder in which the melanocytes or pigment producing cells in the skin are attacked and dye so you loose pigment. There may be some treatments to slow the process but I am unaware of a cure. If you think you have vitiligo see a dermatologist for further eval.