Food allergies: They're not as common as you think

By Michael G. Marcus, M.D. for Your Baby Today

Food allergies are a very common concern among parents. In recent polls, up to 25 percent of parents felt that their children suffered from food allergies. However, when their children were tested only around 5 percent of them were proven to have true food allergies. Why is there this great discrepancy between parental perceptions and actual facts?

For starters, it's easy to blame every rash or hive on a food allergy. And while a food allergy can cause these symptoms, skin reactions are very common in children and can be triggered by a variety of other causes, such as viral infections, harsh soaps, medication, and topical irritants. Only careful testing can accurately isolate the true cause of the reaction.

Other common symptoms of food sensitivity can include abdominal pain, nausea and diarrhea. But again, other causes may also be the culprit. A viral infection of the gastrointestinal tract can frequently cause the above symptoms and actually damage the intestines to the point where a two to four week recovery period is needed for complete healing. In this case, a child may have difficulty digesting certain foods, such as milk, until the intestine is fully healed. Additionally, lactose intolerance, a condition where the body lacks a enzyme needed to properly digest milk products, can also cause these same symptoms.

Finally, nasal congestion, cough and wheeze can occasionally be caused by food allergies, however many other exposures-such as contact with ragweed or pollen-can also result in these same symptoms.

The key to identifying a true food allergy is testing. Three different types of allergy tests are available to accurately identify the food (if any) responsible for the reactions. Skin tests have been used for more than 80 years to pinpoint allergy triggers. These tests are performed by introducing a minute quantity of purified food extract under the skin and observing the reaction after twenty minutes. This test is felt to be 80 to 95 percent accurate.

More recently, a blood test called Radioallergosorbent (RAST) has been used as an alternative to skin testing. The advantage of RAST is that it requires only one to two vials of blood through one needle stick, rather than the 20 or more scratches used in skin testing. The disadvantage is that it is only 80 percent (at best) accurate in its results.

The "gold standard" for testing is a double-blind food challenge. In this test, the patient eats a capsule containing a small quantity of concentrated food without knowing what food is being eaten. If the patient develops the same reaction after two to three challenges with the same food then it is considered a true positive reaction.

Once the offending food is identified, the only acceptable treatment is total avoidance of the food. No other treatment will effectively prevent reactions. Antihistamines can be helpful to relieve symptoms, however, as they wear off the symptoms will frequently return. If the responsible food is avoided for six months to two or more years, then your child will likely be able to tolerate the food when it's repeatedly reintroduced.

Also see:
• Does your child have a cold or are allergies setting in?
• Ask the doctor
• Sick day savvy: How to take care of your child and your career

Michael G. Marcus, M.D., is Director of Pediatric Pulmonology, Allergy and Immunology at Maimonides Medical Center in New York.