Sometimes linked to measles or milk (or anything else, as no-one actually knows!), Crohns is an inflammation of the alimentary canal anywhere between the mouth and anus. it is cyclic, when the affected area is inflamed (think a cobbled instead of a tarmac'ed street), its difficult to absorb foodstuff, and peristalsis is affected. Sufferers have acute pain and diarrhoea, intolerance to certain foods, and need a steroid to keep the inflammation in check. For most sufferers a process of trial and error lets them discover which foods shouldnt be touched with a barge pole - things like onion, preservatives, yoghurt etc are the main triggers in many cases. It's not a fatal disease, my mother has had it for 30 years, but it is debilitating - the long term effects of the cortico steroids are more harmful than the crohns itself.