Over 160 different foods have been identified that can cause allergic reactions in people. Of these, 90% are triggered by the following 8 foods:
- Tree nuts (such as almonds, cashews, walnuts, pine nuts)
- Fish (such as bass, cod, flounder)
Since 2006, the Federal Drug Administration (FDA) has required labeling to identify products that contain any of these 8 allergy-causing foods. Certain foods, however, including fresh produce, fresh meat, and certain oils are exempt from this requirement.
What are the symptoms of a food allergy? Allergic reactions to foods most commonly involve the skin, the digestive tract (stomach and intestines), or the respiratory system (throat and lungs). Skin symptoms include the development of hives, swelling (edema), and redness or flushing. Abdominal pain, nausea, vomiting, and diarrhea are the most common digestive tract symptoms. Respiratory symptoms include sneezing, wheezing, coughing, and runny eyes. The most severe allergic reaction to food is anaphylaxis, also known as anaphylactic shock. Anaphylaxis is a medical emergency that typically affects several areas of the body, including swelling in the throat that may be severe enough to block the airway, a rapid heart rate, and a severe drop in blood pressure. Each year in the U.S., anaphylaxis to food has been estimated to result in 30,000 emergency room visits, 2,000 hospitalizations, and 150 deaths.
Why do food allergies occur? In allergic individuals, certain proteins (allergens) in food are perceived by the body to be harmful. As a response to these allergens, the immune system produces antibodies to protect the body. These antibodies remain in the blood stream following the initial exposure and can recognize the offending protein if the same food is eaten again. Once reactivated, antibodies cause a special type of cell in the bloodstream known as mast cells to release chemicals, including histamine. Histamine is the primary chemical involved in producing allergic symptoms, such as runny nose, itchy eyes, rashes and hives, wheezing, and even anaphylactic shock.
Are all food allergies the same? The allergic features from exposure to different foods vary in many ways, including the specific symptoms produced and their severity, as well as the likelihood for them to become “outgrown”. Often, these unique features can assist the doctor in determining the specific food allergen. Milk allergy is particularly common in children, with cow’s milk being the usual cause. Milk rarely causes anaphylaxis, with the most common symptoms being gastrointestinal in nature (abdominal cramping, diarrhea, etc.). Eggs are another common allergen-causing food during childhood. Fortunately, most children eventually outgrow their egg allergy. Vaccines produced using eggs, such as the influenza vaccine present potential risks to people who have a severe allergy to eggs. Peanuts are legumes, and are thus biologically unrelated to tree nuts. Nevertheless, a number of people with tree nut allergies go on to develop allergy to peanuts also. It is possible for peanut allergy symptoms to occur with skin contact or from eating food that had been exposed to peanuts during their processing. Tree nuts include macadamia nuts, brazil nuts, cashews, almonds, walnuts, pecans, pistachios, hazelnuts, and pine nuts (pignoli or pinon). Tree nut allergies tend to be severe, and are strongly associated with anaphylaxis. Shellfish allergy can occur after eating crustaceans (crabs, lobster, crayfish, shrimp, etc.) or mollusks (clams, mussels, scallops, oysters, squid, etc.). In some people, shellfish allergy occurs with eating only one type of shellfish. Wheat allergy results from the production of antibodies to proteins found in wheat. In people with celiac disease, a specific wheat protein called “gluten” causes an abnormal immune system reaction in the small intestines.
How are food allergies diagnosed? The medical history is the most important diagnostic tool in diagnosing food allergy. A dietary diet, in which a record of the content of each meal is kept, along with any reactions that occurred, can also assist with making the diagnosis. If the medical history and diet information suggests a specific food allergy, specialized testing including allergy skin tests, blood tests, and/or a food challenge can be used to confirm the diagnosis.
How are food allergies treated? There are no medications currently available to treat food allergies. Once identified, the best treatment is to avoid the food that has caused a reaction. This often requires careful attention to the labeling, particularly with foods that do not obviously contain one of the common offenders. For example, pine nuts are a typical ingredient in pesto sauce, and eggs are included in a number of salad dressings. Medications are available for treating allergic reactions should they occur. The most commonly used medications are antihistamines (Benadryl, Allegra, Claritin, others). Inhalers used to treat asthma may also be helpful for people who wheeze during an allergic reaction. With severe reactions such as anaphylaxis, epinephrine, given by injection, can be life saving. People with a history of severe food allergies are advised to carry a self-injecting device loaded with epinephrine (e.g., Epi-pen) for use in the case of an unexpected reaction.