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.