When does a food allergy reaction occur?

Food allergies occur when your body's immune system reacts to a substance in food, usually a protein, your body sees as harmful. This sets off a chain reaction in your body, and symptoms can range from a runny nose and itchy eyes to severe and even life-threatening reactions.

According to the Food Allergy & Anaphylaxis Network "Symptoms may include one or more of the following: a tingling sensation in the mouth, swelling of the tongue and the throat, difficulty breathing, hives, vomiting, abdominal cramps, diarrhea, drop in blood pressure, loss of consciousness, and even death. Symptoms typically appear within minutes to two hours after the person has eaten the food to which he or she is allergic."

A food allergy reaction occurs in two stages, the “sensitization stage” followed by the actual response or “allergic reaction stage.” In the first stage, the food allergens don’t provoke a reaction but rather introduce themselves to the person’s immune system. In response, the immune system creates an army of antibodies that enter the blood. The antibodies attach to mast cells, setting the stage for a potential future allergic reaction.

In the second stage, the reaction stage, occurs when a person eats the food allergens for the second and subsequent times. After they are consumed, the food allergens come in contact with the mast cells. The mast cells release chemicals such as histamine that trigger reactions in the body. The areas in the body that manifest a food allergy reaction are the areas where mast cells are prevalent. In very sensitive individuals, a minute exposure of a food allergen—1⁄44,000 of a peanut, for example—can trigger an allergic reaction.

Reactions can appear as quickly as a few minutes after eating the food. In fact, itchiness in the mouth may occur as soon as the food touches the tongue. After the food reaches the stomach and begins to be digested, vomiting and/or diarrhea may result. When they enter the blood, the food allergens can cause a drop in blood pressure. When the allergens are near the skin, hives can develop, and as the allergens make their way to the lungs, asthma can ensue.