While an estimated 40 to 50 million Americans have allergies, only one to two percent of all adults are allergic to foods or food additives. Eight percent of children under age six have adverse reactions to ingested foods but of that 8%, only 2-5% have confirmed food allergies.
What are the symptoms of a food allergy?
Allergic reactions to foods typically begin within minutes to a few hours after eating the offending food. The frequency and severity of symptoms vary widely from one person to another. Mildly allergic persons may suffer only a runny nose or sneezing, while highly allergic persons may experience severe and life-threatening reactions.
The most common symptoms of food allergy involve the skin and intestines. Skin reactions include rashes (hives and eczema), while intestinal symptoms typically include vomiting, nausea, stomach cramps, indigestion and/or diarrhea. Other symptoms can be swelling of the tongue, lips or throat; asthma, with coughing or wheezing; rhinitis, often including itchy, stuffy, runny nose and sneezing; loss of blood pressure; and rarely, anaphylaxis, a severe allergic reaction that may be life threatening.
Because these symptoms can be caused by a number of different diseases other than food allergy, your physician may want to evaluate you to rule out the source of your problem.
What causes my symptoms?
A food allergy is the result of your body’s immune system over-reacting to food proteins called allergens. Normally your immune system protects the body against allergic reactions; however, in the individual with food allergy, the immune system produces increased amounts of the allergic antibody called immunoglobulin E, or IgE. When these antibodies combine with food allergens, histamine and other chemicals are released as part of the body’s immune reaction. These chemicals can cause blood vessels to dilate, muscles to contract and affected skin areas to become red, itchy and swollen. These IgE antibodies can be found in different body tissues—skin, intestines and lungs—where specific allergy symptoms such as hives, vomiting, diarrhea and wheezing occur.
Not all adverse reactions to foods are due to allergy. Some reactions to cows’ milk, for example, are related to a deficiency of an enzyme (lactase) that normally breaks down a sugar in milk (lactose). When individuals with lactase deficiency drink cows’ milk or eat other dairy products, they may experience intestinal symptoms, the most common examples include stomach cramping, gas and diarrhea. This is sometimes misinterpreted as a food allergy.
Why do I have a food allergy?
Although food allergy occurs most often in infants and children, it can appear at any age and can be caused by foods that had been previously eaten without any problems. Excessive exposure to a particular food may affect the overall rate of allergy to that food as well.
Which foods are most likely to cause a food allergy?
Nine basic foods are responsible for 95% of food allergies. They include: egg, wheat, corn, milk, fish, shellfish, soy, nuts and tree nuts, but almost any food has the potential to trigger an allergy.
Keep in mind that if you are allergic to a particular food you might be allergic to related foods. For example, a person allergic to walnuts may also be allergic to pecans and persons allergic to shrimp may not tolerate crab and lobster. However, complete restriction of all “related” foods based on an allergy is rarely necessary.
Note: Oral allergy syndrome or OAS is a type of food allergy noted by allergic reactions in the mouth. The most common reaction is an itching or burning sensation in the lips, mouth, ear canal, and/or pharynx. Sometimes other reactions can be triggered in the eyes, nose, and skin. Swelling of the lips, tongue and uvula and a sensation of tightness in the throat may be observed. Notify your doctor if you notice any of these symptoms.
How does an allergist know which foods make me sick?
Some people know exactly what food causes their allergic symptoms. They eat peanuts or a peanut-containing product and immediately break out with hives. Other individuals need their allergist’s help in determining the “culprit,” especially when the specific food cannot be identified or when the symptoms show up many hours after ingesting an offending food.
Your allergist will typically begin by taking a comprehensive medical history. You’ll be asked about the symptoms you experience following the food ingestion, how long after the food ingestion they occurred, how much of the offending food was ingested, how often the reaction has occurred and what type of medical treatment, if any, was required. Moreover, you will be asked about your overall diet, your family’s medical history and your home environment. These questions are necessary for your allergist to eliminate the possibility that another problem or allergic condition may be causing or adding to your symptoms.
What is allergy testing?
You may be asked to undergo some allergy testing to clarify your diagnosis. Your allergist will likely use a skin test, in which a diluted amount of the appropriate food extract is placed on the skin and the skin is then lightly scratched. This procedure is safe and generally not painful. Within 15 to 20 minutes, a positive reaction typically appears as a raised bump surrounded by redness, similar to a mosquito bite, and indicates the presence of allergic antibodies to the particular food. In some cases, an IgE blood test can be used to provide similar information, but it is generally more expensive than skin testing and the results are usually not available immediately. If properly performed and interpreted, skin tests to foods are reliable and good screening tests. However, it’s entirely possible to test “allergic” to a food (by skin testing or IgE blood testing) and yet have no symptoms when that food is eaten. Therefore confirmation requires appropriately designed oral challenge testing with each suspected food.
Can food allergies be determined by a special diet?
Sometimes. Your allergist may further narrow down the suspected foods by placing you on a special diet. If your symptoms occur only occasionally, the culprit is likely a food that is eaten infrequently. Your allergist may ask you to keep a daily food diary listing all food and medication ingested along with your symptoms for the day. By reviewing and comparing “good days” with “bad days,” you and your allergist may be able to determine which food is causing your reaction.
If only one or two foods seem to be causing allergic reactions, it may be necessary for you to go on a food elimination diet. The suspect food must be completely eliminated in any form for a short time—one to two weeks. If the allergic symptoms subside during abstinence and flare up when the food is ingested again, the likelihood of identifying the problem food can be increased.
If several foods appear to cause problems, your allergist may want to confirm the role of each suspected food by oral food challenge testing. Not all positive skin tests or IgE blood tests confirm a definite food allergy. With this in mind, food challenges are the best way to determine whether or not a food allergy really exists.
During an oral food challenge test you will eat or drink small portions of a suspected food in gradually increasing portions over a given period of time under a physician’s supervision to see if an allergic reaction occurs.
What if I accidentally eat something I'm allergic to?
Individuals with food allergy should have a clearly defined plan of action for handling situations in which they accidentally ingest a food allergen. Why? Because on average people who have removed peanuts from their diets for allergic reasons are likely to accidentally ingest one every three years. That’s why it’s important to have a list of symptoms and your doctor’s instructions for treatment posted in a prominent place in your kitchen. Oral antihistamines can be very useful in treating many of the early symptoms of a mild allergic reaction to a food, too.
People with histories of severe reactions need to be instructed in when and how to give themselves a shot of epinephrine (adrenaline) in the event of a severe allergic reaction. This medication is available in easy-to-use injectable devices, such as an EpiPen, and should be carried by people with histories of severe allergic reactions. You should be taken to the hospital or call 911 and arrange for follow-up medical care for a severe reaction. Bracelets or necklaces may be worn to quickly alert medical personnel or other caretakers about food allergies.
Patients who use caution and carefully follow an allergist’s advice can bring food allergy under control. Contact your physician with further questions and concerns about food allergy.
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How are food allergies treated?
Once the diagnosis of food allergy is confirmed, the most effective treatment is to avoid eating the offending food in any form. Carefully check ingredient labels and learn other names for the food or food additive to make sure it is not present. When you eat in a restaurant, you must be particularly careful and you should take emergency medicines with you if you have a history of severe reactions. Waiters (and sometimes the kitchen chef) are not always aware of the exact ingredients of items on the restaurant’s menu.
All patients with food allergies must make some changes in the foods they eat. Special food allergy cookbooks, patient support groups and registered dietitians can provide valuable assistance regarding your diet.
Why should I see an allergist?
An allergist/immunologist is a pediatrician or internist with at least two additional years of specialized training in the proper diagnosis and treatment of allergic diseases.
The right care can make the difference between suffering with food allergies and feeling better. By visiting the office of an allergist, you can expect an accurate diagnosis, a treatment plan that works and educational information to help you properly identify and manage your food allergies.
Can you outgrow food allergies?
Most children outgrow cow’s milk, egg, soy and wheat allergy, even if they have a history of a severe reaction. About 20% of children with peanut allergy will outgrow it, and about 9% of children with tree nut allergy will eventually no longer have reactions. Your allergist can help you learn when your child might outgrow a food allergy.
In some cases, particularly in children, strict adherence to an elimination diet seems to help them outgrow a food allergy. For example, the vast majority of patients with documented allergic reactions to eggs, cows’ milk and soy eventually become tolerant to these foods. Allergies to peanuts, tree nuts, fish and shellfish, however, typically last a lifetime and are not outgrown.
Sometimes an allergist may obtain blood work and repeat skin testing to find out if you have outgrown your food allergy. If the skin test and blood test are no longer positive, your allergist may recommend that you undergo an oral food challenge under observation to reassess your symptoms. If you have no reaction and can ingest a normally prepared portion of the food, you may be able to safely reintroduce this food into your diet. If any symptoms of an allergic reaction do occur, the dietary restriction will need to be continued.