How long can it take for a food allergy to manifest?

I'm looking for clinical studies or expert opinion (board certified allergists) on how long it can take for an allergic reaction to appear after the allergen has been eaten. So far, most articles and books on the subject of allergies and food allergies brush over that detail. Most say an allergic reaction can take up to 4 hrs or 6 hrs. Once in a while an "expert" who is not an allergist will say it can take 24 to 48 hours. Has anyone actually studied it in double blind environment?

I was not allergic to shell fish (particularly shrimp) until I was 11 or 12 years old. Before that, I never had a problem.

This is actually not what I was asking. I'm not looking for how long it can take to discover you have an allergy but how long, if you do have one, it might take to "show" after you've eaten a trigger. Report It

I am not an immunologist, but board-certified Internist. Allergic responses take as little as seconds up to days. This depends on the histamine response, degree of sensitivity as well as the method of absorption...nasal, ingestion, or injection or skin contact. Anaphylaxis of penicillin or other injected drugs is very rapid, whereas response to dandruff of animals take an hour or so, and some contact allergens take 48 hours or even long. There are numerous studies available both in Immunology or Dermatology (Dermatologists get about 1/3 of allergic responses). For definitive studies, consult any of the major texts on immunology available in medical libraries or try the AMA for a bibliography of the more current studies.

All I know is that my allergist told me that it would manifest itself within two hours of consumption. I thought I was allergic to sesame seeds, but I had eaten them at 10:30 in the morning, again at 1:00 in the afternoon and I was in anaphalactic shock by 3:15. He said if it was sesame seeds, I would have been sick before 3:00. All my other food allergies have come on within minutes of eating.