White tongue can be due to following reasons - 1)Dehydration 2)Poor oral hygiene 3)Illness or infection 4)Dry mouth 5)Candida yeast infection (oral thrush) The commonest cause is dehydration or dry mouth which is breeding ground for bacteria. In fact if you don't brush your tongue and teeth twice a day you are increasing the risk of white tongue. White tongue is also due to an overgrowth of candida , a fungus that causes can didi as candidiasis or oral thrush.It can be scraped off by peeling.