Do food allergies start suddenly like when you are eating?

Maybe: The more significant the allergy, the quicker the response. Food allergies often manifest with itching or swelling in the mouth while eating; once swallowed, there may be abdominal cramping. Bloating, nausea, vomiting, or diarrhea. Acute, severe reactions can cause hives, wheezing and loss of blood pressure, but milder, chronic allergy & ingestion can cause rashes such as eczema.