People with allergies have over-reactive immune systems that target and react to otherwise harmless substances in food or the environment. Food allergies are defined by an immune response triggered by food proteins. A substance that elicits an allergic response in an individual is called an "allergen." The severity of a reaction depends upon how sensitive an individual is and the quantity of the allergen consumed.
When a susceptible individual is exposed to a food allergen, the immune system reacts by releasing chemical "mediators" such as histamine. These chemical mediators trigger mild to severe inflammatory reactions in the tissues of the skin (itching, hives, rash), the respiratory system (cough, difficulty breathing, wheezing), the gastrointestinal tract (vomiting, diarrhea, abdominal pain), and/or the cardiovascular system (decreased blood pressure, heartbeat irregularities, shock).
When the symptoms of allergy develop rapidly, are severe and wide-spread, and occur in one or more systems of the body, the reaction is termed "anaphylaxis." Anaphylaxis is a life-threatening event that occurs in allergic individuals after exposure to their specific allergens. Food is the most common trigger of anaphylaxis in the general community and can be fatal if not treated immediately.
Aside from foods, other common examples of life-threatening allergens are: stinging insects, medications, and latex rubber. Anaphylaxis may also occur in association with exercise. Approximately 150-200 deaths per year are due to food anaphylaxis, mostly from peanut and tree nut allergies, while 50 deaths per year are caused by insect stings. According to a study released in 2013 by the Centers for Disease Control and Prevention, food allergies among children increased by approximately 50% between 1997 and 2011. Fatal anaphylaxis is more common in children with food allergies who are asthmatic, even if the asthma is mild and well controlled.