<<Disclaimer: Verify this information before applying it to your situation.>> Whenever I experience an allergic reaction, the visible symptoms begin approximately two days after ingestion. This has been extremely consistent for 30 years. Andrew Jean Jasinski wrote: > One of the basic premises of food allergies is that a reaction is > not always immediate. In fact, it can take up to 72 hours for > a reaction to show up although it is very difficult to pin a reaction > 72 hours later on one food you ate three days ago. We've seen > reactions that can be directly attributed to food 10-14 hours later > (like tomato sauce eaten at dinner causing a bad tantrum at school > the next day).