Don't know!! It runs in my family and can be triggered by stress, but it's genetic. It may be an autoimmune reaction. As far as autoimmune reactions go, it's one of the more mild ones (compared to lupus and scleroderma, for instance). I don't know of a prevention or a cure. A dermatologist may have a treatment that will reverse or at least stop it. But you definitely need to stay out of the sun forever.
Thank you for your reply,
the interesting thing about Vitiligo is that it is not very common in the US compared to Middle Eastern countries. I lived in the US for many years and I've only seen one case and it was a Middle Eastern man. Having lived in a Middle Eastern country, I can testify that it is very common.... It is probably as you said hereditary!
My uncle once had a small spot in his face but he used some traditional medicine and they were able to stop it from spreading to the rest of his body....