Allergen

The body’s immune system keeps us healthy by fighting off infections and other dangers to good health. A food allergy reaction occurs when our immune system overreacts to a food or a substance in a food, identifying it as a danger and triggering a protective response.

While allergies tend to run in families, it is impossible to predict whether a child will inherit a parent’s food allergy or whether siblings will have a similar condition.

Symptoms of a food allergy can range from mild to severe. Just because an initial reaction causes few problems doesn’t mean that all reactions will be similar; a food that triggered only mild symptoms on one occasion may cause more severe symptoms at another time.

The most severe allergic reaction is anaphylaxis — a life-threatening whole-body allergic reaction that can impair breathing, cause a dramatic drop in blood pressure and affect heart rate. Anaphylaxis can come on within minutes of exposure to the trigger food. It can be fatal and must be treated promptly with an injection of epinephrine (adrenaline).

While any food can cause an adverse reaction, eight types of food account for about 90 percent of all reactions:

•  Eggs

•  Milk

•  Peanuts

•  Tree nuts

•  Fish

•  Shellfish

•  Wheat

•  Soy

Certain seeds, including sesame and mustard seeds, also are common food allergy triggers and considered a major allergen in some countries.

Symptoms of an allergic reaction may involve the skin, the gastrointestinal tract, the cardiovascular system and the respiratory tract. They can surface in one or more of the following ways:

•  Vomiting and/or stomach cramps

•  Hives

•  Shortness of breath

•  Wheezing

•  Repetitive cough

•  Shock or circulatory collapse

•  Tight, hoarse throat; trouble swallowing

•  Swelling of the tongue, affecting the ability to talk or breathe

•  Weak pulse

•  Pale or blue coloring of skin

•  Dizziness or feeling faint

Anaphylaxis, a potentially life-threatening reaction that can impair breathing and send the body into shock; reactions may simultaneously affect different parts of the body (for example, a stomachache accompanied by a rash)

Most food-related symptoms occur within two hours of ingestion; often they start within minutes. In some very rare cases, the reaction may be delayed by four to six hours or even longer. Delayed reactions are most typically seen in children who develop eczema as a symptom of food allergy and in people with a rare allergy to red meat caused by the bite of a lone star tick.

source : 

American College of Allergy, Asthma & Immunology   http://acaai.org/allergies/types/food-allergies