Hi - My husband's allergy to casein came on suddenly at the age of 23. He had previously developed lactose intolerance (which is rare in children under age 5, but steadily increases in the population as people get older). He had no particular illnesses immediately prior to the onset of milk allergy (unless you could entering graduate school as an illness :-). His tolerance has increased slightly, though. In the beginning, his tolerance for milk protein was zero. He can now get away with tiny amounts (the kind you get through cross-contamination, or an incautious single bite of a cookie) without excessive difficulty. I hope this helps, --Beth Kevles [log in to unmask] http://web.mit.edu/kevles/www/nomilk.html -- a page for the milk-allergic Disclaimer: Nothing in this message should be construed as medical advice. Please consult with your own medical practicioner.