A food allergy is a condition in which certain foods trigger an abnormal immune response (2Trusted Source).It's caused by your immune system wrongly recognizing some of the proteins in a food as harmful. Your body then launches a range of protective measures, including releasing chemicals like histamine, which causes inflammation.For people who have a food allergy, even exposure to very small amounts of the problem food can cause an allergic reaction.Symptoms can occur anywhere from a few minutes after exposure to a few hours later, and they may include some of the following:Swelling of the tongue, mouth or faceDifficulty breathingLow blood pressureVomitingDiarrheaHivesItchy rash