First, we must clearly define what it means to have a food allergy. A diagnosis of food allergy implies an adverse reaction to food occurred due to an immune response. Not all adverse reactions to foods involve the immune system and thus are not true food allergies. In fact, food allergies are only a fraction of all adverse food reactions. Adverse food reactions that do not involve the immune system include lactose intolerance, pharmacologic reactions, food poisoning, and toxic reactions. Immunological mediated food allergies can be classified according to what role the immune system plays in the reaction. Food allergies are either IgE antibody mediated or mediated by cells of the immune system. IgE antibody mediated reactions can affect various organs of the body and can be life threatening. Most commonly the skin is affected with hives but also flushing and itching can occur. Swelling of the lips and tongue and difficulty breathing or wheezing can occur and patients with uncontrolled asthma are at increased risk for a severe reaction. Vomiting, nausea, abdominal cramps with pain and occasionally diarrhea are also seen with IgE mediated reactions. Anaphylaxis, the most severe consequence of food allergies involves multiple organs and can lead to collapse of circulation, a life threatening situation.

Just as with all other allergic diseases, food allergies are occurring more frequently. You may read information in the newspaper, on the internet, or hear about other friends’ or families’ experiences with food allergies. Patients many times have common misconceptions regarding food allergies. This introduction will hopefully clearly explain food allergies and clarify any confusion you may have regarding diagnosis and treatment options.

First, we must clearly define what it means to have a food allergy. A diagnosis of food allergy implies an adverse reaction to food occurred due to an immune response. Not all adverse reactions to foods involve the immune system and thus are not true food allergies. In fact, food allergies are only a fraction of all adverse food reactions. Adverse food reactions that do not involve the immune system include lactose intolerance, pharmacologic reactions, food poisoning, and toxic reactions. Immunological mediated food allergies can be classified according to what role the immune system plays in the reaction. Food allergies are either IgE antibody mediated or mediated by cells of the immune system. IgE antibody mediated reactions can affect various organs of the body and can be life threatening. Most commonly the skin is affected with hives but also flushing and itching can occur. Swelling of the lips and tongue and difficulty breathing or wheezing can occur and patients with uncontrolled asthma are at increased risk for a severe reaction. Vomiting, nausea, abdominal cramps with pain and occasionally diarrhea are also seen with IgE mediated reactions. Anaphylaxis, the most severe consequence of food allergies involves multiple organs and can lead to collapse of circulation, a life threatening situation.

There are several characteristics of IgE mediated reactions that are very helpful in determining if a reaction is due to a specific food. Usually only a few minutes passes between consumption of an allergenic food and the reaction. Rarely, a few hours may pass before symptoms appear but if more than 4-6 hours has passed without problems, an IgE mediated reaction is unlikely. Without continued exposure to the allergenic food symptoms from an IgE mediated reaction do not typically persist. Occasionally, with severe reactions symptoms may linger but usually not longer than 24 hours. Finally, IgE mediated reactions should be reproducible (reoccur) with subsequent ingestion of the problem food. Symptoms may be different but if they don’t occur with consumption of an adequate amount of the food then it is unlikely that the food is a problem.

The other type of immunological mediated food reactions is called cell mediated food allergies. Our knowledge of these types of food allergies is not as extensive as IgE mediated food allergies. Just like IgE mediated reactions cell mediated reactions can affect several different organ systems but the GI tract is most commonly involved. Symptoms include vomiting, diarrhea, blood in the stool, and in severe reactions, patients may develop dehydration as a result of profuse vomiting and diarrhea. There are several distinguishing features of cell mediated food allergy reactions that clearly differentiate these from IgE mediated food allergies. Cell mediated food allergy reactions are much less common. Unlike IgE mediated reactions, which occur immediately after exposure these reactions are delayed between 2 to 12 hours and rarely may occur up to 24 hours later. Milk and soy are most commonly implicated but other foods including grains have been identified as causing cell mediated food allergies.

Several other conditions may also be related to food allergies. Atopic Dermatitis (AD)or eczema is a condition of the skin with itch leading to redness, scratching, scaling and thickening of the skin. Thirty to 50% of patients with moderate to severe AD have food allergies. Avoidance of allergic foods typically allows for better control of the skin symptoms. Food allergy in AD is thought to be related to a combination of both IgE and cell mediated mechanisms. Thus, symptoms may be either immediate or delayed. Eosinophilic disorders of the gastrointestinal tract may also be related to food allergies. Symptoms may be similar to gastroesophageal reflux disease (heartburn) but can also include the feeling of food getting stuck in the esophagus and abdominal pain. These disorders are diagnosed by detecting eosinophils in the lining of the GI tract. Food allergies are suspect to play a role in this disorder.

Testing to detect the presence of IgE antibodies that are specific to the suspect food allows your doctor to confirm food allergy. There are currently two types of testing available to detect IgE food allergies. Traditional allergy skin testing and a blood test called CAP RAST both provide valuable information for diagnosing and managing food allergy. Many times it may be necessary to have both of these evaluations conducted. Testing is indicated only when there is a history suspect for food allergy. We may suggest a food challenge, to the suspect food, if the history does not clearly suggest food allergies and testing is inconclusive. Food challenges should always be conducted in a controlled medical environment with personnel and equipment needed to treat allergic reactions.

Treatment of food allergies involves strict avoidance of known food allergies. Currently, avoidance is the only treatment available for food allergies. With avoidance, many children will be able to eventually tolerate their allergic foods. Even foods such as peanut, which were once thought to cause lifelong allergy, may be “outgrown” by some individuals. Patients with food allergies are instructed to read and check food labels carefully for the presence of food allergens. Due to the confusing labeling practices of food manufactures, it is important for patients with food allergies to be educated to identify specific foods. Hopefully new legislation will be passed requiring uniform labeling practices, which should help reduce accidental ingestions. All patients with IgE mediated food allergies should be prescribed epinephrine (Epi Pen) and instructed on the treatment of severe allergic reactions due to food allergies. Epi Pen is the only potential life saving treatment available for severe allergic reactions. In reviewing fatalities from food allergies, many times epinephrine was not used or administration was delayed. Many patients mistakenly assume that their reactions to foods will never be serious since previous reactions were minor. We know from large studies that previous reactions do not predict with any certainty future reactions. You should always be prepared for a severe reaction by carrying an Epi Pen at all times.