I don't believe that chronic nail biting contributes to the acquisition of Crohn's Disease--but I've wondered for a long time if it doesn't exacerbate the disease. I bite my nails like crazy, and I tend to swallow the nail bits. If husks, seeds, nuts, and peels can irritate the intestinal wall and stimulate inflammation, I'm sure that little bits of hard fingernail do the same thing. I've always wondered if any studies (or any doctors) have addressed this issue. Thanks for bringing up a quirky but interesting subject that I've never seen mentioned by anybody.