What is the white hair growing on my arms and face? I'm anorexic and I think thats something that happens but what is it called and why does it happen?

Lanugo. In anorexia, growth of a fine downy hair, often light in color, is characteristic. This is referred to as lanugo. The precise origin is unclear and may be an adaptive response to hold in body heat or may represent a response to the disorder in hormone production.