Re: white patch in black hair??
For some reason, the follicles of the hairs affected are receiving no melanin. This poses no health threat but understandably can cause one to worry.
I did know someone who had this, many years ago. He was in my class at school and we were 12. It happened shortly after he was in a terrible car accident but nobody knew why, so they passed it off as stress. The oddest thing about it all was that the patch he had on his head was exactly the same patch that his dog had, on it's head! Same patch and size! Those who did not know this boy actually thought he had dyed his hair to match his pet!