According to NPR, the upcoming edition of the the American Psychiatric Association's DSM (Diagnostic and Statistical Manual of Mental Disorders) will put "pathological grooming" in the same category as obsessive compulsive disorder. Pathological grooming includes nail biting, hair pulling, and skin picking.
Previously, these were in a category called "not otherwise classified". The new proposal puts obsessive grooming in the same category of obsessive compulsive behavior along with other things like hoarding and body dysmorphia disorders.
Bad news for me, since I've always had some sort of nervous habit that I thought was perfectly normal.