The ABCs of Food Allergies
Approximately 8% of children and 2% of adults suffer from true food allergies. When the culprit food is eaten, most allergic reactions will occur within minutes. Skin symptoms (itching, urticaria, angioedema) are the most common, and occur during most food reactions. Other symptoms can include nasal (sneezing, runny nose, itchy nose and eyes), gastrointestinal (nausea, vomiting, cramping, diarrhea), lung (shortness of breath, wheezing, coughing, chest tightness), and vascular (low blood pressure, light-headedness, rapid heart beat) symptoms. When severe, this reaction is called anaphylaxis, and can be life threatening.
Allergy or Intolerance?
Most reactions to food are probably not allergic in nature, but rather intolerance.
This means that there is no allergic antibody present against the food in the person. Intolerance can be classified as toxic and non-toxic. Toxic reactions would be expected to occur in most people if enough of the food was eaten, examples include alcohol, caffeine or in cases of food-poisoning. Non-toxic food intolerance occurs only in certain people, such as lactose intolerance, which is due to the deficiency of lactase, the enzyme which breaks down the sugar in milk and dairy foods. Patients with lactose intolerance experience bloating, cramping and diarrhea within minutes to hours after eating lactose-containing foods, but do not experience other symptoms of food allergies.
Non-allergic Immunologic Reactions
A less common form of non-allergic reactions to food involves the immune system, but there are no allergic antibodies present. This group includes celiac sprue and FPIES (food protein induced enteropathy syndromes). FPIES typically occurs in infants and young children, with gastrointestinal symptoms (vomiting, diarrhea, bloody stools, and weight loss) as the presenting signs. Milk, soy and cereal grains are the most common triggers in FPIES. Children typically outgrow FPIES by 2 to 3 years of age.
Common Childhood Food Allergies
Milk, soy, wheat, egg, peanut, tree nuts, fish and shellfish compromise more than 90 percent of food allergies in children. Allergy to milk and egg are by far the most common, and are usually outgrown by age 5 years. Peanut, tree nut, fish and shellfish allergies are typically the more severe and potentially life-threatening, and frequently persist into adulthood.
Cross-Reactivity and Cross-Contamination
Cross-reactivity refers to a person having allergies to similar foods within a food group. For example, all shellfish are closely related; if a person is allergic to one shellfish, there is a strong chance that person is allergic to other shellfish. The same holds true for tree-nuts, such as almonds, cashews and walnuts.
Cross-contamination refers to a food contaminating another, unrelated food leading to a "hidden allergy". For example, peanuts and tree nuts are not related foods. Peanuts are legumes, and related to the bean family, while tree nuts are true nuts. There is no cross-reactivity between the two, but both can be found in candy shops and in a can of mixed nuts, for instance.
Diagnosing Food Allergies
The diagnosis is made with an appropriate history of a reaction to a specific food, along with a positive test for the allergic antibody against that food. Testing for the allergic antibody is typically accomplished with skin testing, although can be done with a blood test as well.
The blood test, called a RAST test, is not quite as good of a test as skin testing, but can be helpful in predicting if a person has outgrown a food allergy. This is especially true since in many cases the skin test can still be positive in children who have actually outgrown the food allergy.
If the diagnosis of food allergy is in question despite testing, an allergist may decide to perform an oral food challenge for the patient. This involves having the person eat increasing amounts of food over many hours under medical supervision. Since the potential for life-threatening anaphylaxis exists, this procedure should only be performed by a physician experienced in the diagnosis and treatment of allergic diseases. An oral food challenge is the only way to truly remove a diagnosis of food allergy in a patient.
Managing Food Allergies
Treat the reaction: If a reaction to the food is present, the person should seek immediate emergency medical care. Most patients with food allergies should carry a self-injectable form of epinephrine, or adrenaline (such as an Epi-pen®, with them at all times. These medications can be prescribed by a physician and the patient should know how to use this device before an allergic reaction occurs.
Avoid the food: This is the main way to prevent future reactions to the culprit foods, although can be difficult in cases of common foods such as milk, egg, soy, wheat and peanut. Organizations such as the Food Allergy and Anaphylaxis Network offer help and support to patients and parents of children with food allergies.
Allergy physicians can also offer additional information and advice on avoidance.
Read food labels: Since accidental exposure to the allergic food is common, reading labels on foods and asking questions about ingredients at restaurants is important and recommended.
Be prepared: Patients with food allergies should always be prepared to recognize and treat their reaction, should one occur. Remember, since exposures to the allergic foods are frequently accidental, being prepared to treat the reaction with epinephrine is paramount. Emergency medical care should always be sought if an allergic reaction to food occurs, whether or not epinephrine is used.
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