Overview of Food Allergies
A food allergy is an abnormal immune system response that is triggered by sensitivity to a substance in a certain food. These substances, which are called allergens, usually do not cause a reaction in most people.
Almost any food can cause an allergy. Common food allergy causes include eggs, milk, peanuts, fish, soy, wheat (called celiac disease or gluten-induced enteropathy), shellfish (e.g., lobster, crab, shrimp), and nuts (e.g., walnuts, almonds, cashews). In some cases, consuming even a trace amount of the food can cause an allergic reaction.
When a person with a food allergy eats a food to which he or she is allergic, the immune system mistakenly identifies a substance in the food (e.g., a protein) as harmful. It then activates a response to counteract the effect of (neutralize) or destroy the substance. This immune system response involves producing antibodies (e.g., immunoglobulin E [IgE]) and releasing chemicals (e.g., histamine) and enzymes (e.g., proteinase) that cause allergy symptoms.
Food allergy symptoms usually develop within minutes to 1 hour of exposure to the allergen. Common symptoms include itching, swelling, rashes, vomiting, abdominal pain, and wheezing.
A severe allergic reaction can result in a life-threatening condition called anaphylaxis (pronounced ăn-uh-fuh-LĂK-sĭs). Anaphylaxis, also called allergic cascade, is a medical emergency. This condition develops quickly and affects several body systems (e.g., respiratory system, nervous system). Anaphylaxis may cause difficulty breathing, hives (urticaria), low blood pressure (hypotension), loss of consciousness, and death.
There are several different types of adverse reactions to food (called food hypersensivities) and food allergies are just one type. Food hypersensitivities can cause similar symptoms; however, most adverse reactions to food are not caused by a true food allergy.
Adverse reactions to food that do not result in an immune system response are called non-allergic food hypersensitivities. Types of non-allergic food hypersensitivities include food intolerances (e.g., lactose intolerance), sensitivities to chemicals (e.g., histamine in cheese, wine, tuna) and additives (e.g., sulfites, monosodium glutamate [MSG]) in food, and food poisoning (caused by eating food contaminated with microorganisms [e.g., bacteria] and harmful toxins). Food allergies can be differentiated from non-allergic food hypersensitivities through diagnostic testing.
Incidence and Prevalence of Food Allergies
The exact prevalence of food allergies is unknown. According to the Food and Drug Administration (FDA), the American Academy of Allergy Asthma & Immunology (AAAI), and the World Health Organization (WHO), food allergies affect approximately 13% of all adults. In the United States, it is estimated that about 67 million people have a food allergy.
Food allergies are more common in children younger than 3 years of age. In the United States, about 2 million children in this age group (about 48%) have a food allergy. Food allergies affect boys more often than girls.
In the United States, the incidence of food allergies (e.g., peanut allergy) and other related conditions, such as asthma and hay fever, has increased dramatically in recent years. According to the Centers for Disease Control and Prevention (CDC), approximately 1 child in 26 had a food allergy in 2007, compared to 1 in 29 children in 1997. The reason for this is unknown; however, it may be related to prenatal (before birth) exposure to allergens, to genetic factors (i.e., family history of allergies), or to higher levels of additives in foods and other products, such as lotions.