MILWAUKEE (AAAAI) -- Allergic reactions to carrot and celery are very uncommon in the United States, however, reactions to carrots affect up to 25 percent of food-allergic individuals in Europe, and are associated with cross sensitivity to celery, certain spices, mugwort, and birch pollen. Several European researchers were recently able to prove the allergenicity of carrot for the first time in a study from the August Journal Allergy and Clinical Immunology.

Barbara Ballmer-Weber, MD, and colleagues from University Hospital in Zurich, Paul-Ehrlich-Institut, Langen, Germany and the University of Vienna, sought to confirm sensitization to carrot by conducting several different tests on 26 patients with a history of allergic reactions to carrots.

Two food challenges were performed. The first was a double-blinded, placebo-controlled food challenge (DBPCFC), where subjects were given two different drinks: one was an active drink containing carrot and the other was a placebo drink. The second food challenge performed was a spit and chew test. The patients with a negative reactions in the DBPCFC chewed 5 g of raw carrot and spit it out. If they did not experience a reaction, they chewed and swallowed 5 g, then 10 g, and then 20 g of raw carrot. Skin tests and in vitro blood tests were performed to check for the presence of IgE, the antibody that produces allergic reactions. In vitro testing was also performed to see if allergic sensitivity to birch pollen initially triggered the sensitivity to carrots in these individuals.

In the first food challenge, researchers found that 20 patients reacted to the carrot-containing drink but not the placebo. Four patients responded to neither the carrot-containing drink nor the placebo drink. In the spit and chew test, three of these latter four subjects noted no symptoms. The fourth patient reported symptoms of oral allergy syndrome (itching of the throat and mouth) after swallowing 5 g of raw carrot. Researchers found that all patients who had positive DBPCFCs also had positive skin test results to raw carrot, while all patients who had negative DBPCFC's had negative skin tests and did not have subsequent reactions to the ingestion of carrot. Additionally, all of the carrot-allergic patients also had birch pollen specific IgE. However, in vitro testing of the serum from the carrot-allergic patients revealed that allergic binding could not be blocked by birch pollen proteins.

For the first time researchers were able to confirm carrot allergy in 20 of 26 European patients using DBPCFC protocol with carrot. Although these allergic patients produced IgE to both carrot and birch pollens, in vitro testing seemed to discount the theory that exposure to airborne birch pollen always precedes and predisposes allergic patients to the development of carrot allergies.