Think you have food allergies? Think again

In people with allergies, IgE triggers the release of histamines and other chemicals that can lead, within minutes to two hours, to a variety of symptoms, including itchy mouth, swollen tongue, hives, wheezing, skin rashes, nausea, vomiting and diarrhea. At its worst, the reaction is anaphylaxis -- a potentially life-threatening reaction that can occur within seconds and may lead to shock, airway closure and a blood-pressure drop.

In the case of food, these reactions appear to be happening more often than they used to. Exact comparisons are hard to come by, but some studies show a doubling of peanut allergies in the last five to 10 years in kids in the U.S., United Kingdom and Australia. A Mayo Clinic study published in June reported that celiac disease is now four times more common than it was in the 1950s.

For all food allergies, diagnoses in U.S. kids have increased by 18% in the last decade, according to the Centers for Disease Control and Prevention.

Inaccurate tests

As food allergies become more common, doctors struggle to figure out who actually has them. Testing is part of the problem: Common food allergy tests aren't very accurate.

The only sure-fire way to test for food allergies is with food challenges, in which patients consume controlled and increasing doses of a suspected food under careful supervision.

Yet doctors, especially primary care doctors who aren't allergy specialists, are far more likely to do blood tests, which are much less accurate and more difficult to interpret.

Experts have seen a proliferation of blood testing by primary doctors, a trend that leads to misdiagnoses of food allergies.

"We get patients coming in who are avoiding 20 or 30 foods based on blood tests," says David Fleischer, a pediatric allergist at National Jewish Health in Denver.

In a recent study, Fleischer and colleagues spent two weeks working with 125 children who had been diagnosed with a collective total of 60 food allergies. The kids, whose average age was 4, took a series of food challenges.

At the end of the study, presented in March at an allergy conference, the researchers were able to reintroduce at least four and as many as 20 foods into each child's diet. About 90% of the suspected allergies had turned up negative.

"People are so happy and appreciative when they can get more foods in," Fleischer says. "Even just one food allergy changes your life."

Celiac disease