Ketchup and mustard are must-have burger and hot dog accompaniments, and they add zip to french fries and pretzels. For many people, however, the tiniest smear of ketchup or mustard can mean a serious allergic reaction. Because both condiments are loaded with potential allergens, discerning the source of a ketchup or mustard allergy is best left to professional testing by an allergist.
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Approximately 1 percent of children with food allergies are allergic to mustard, according to Clinical Immunology and Allergology researchers in Nancy, France. Their findings, published in the April 2003 edition of the journal "Allergy," found that skin prick tests using ground mustard seeds or mustard seasoning produced stronger skin reactions than allergenic mustard extract. The significant mustard allergen is the seed protein 2S albumin. It remains allergenic even when processed.
A study from Madrid's Laboratorios LETI, reported in the March 2011 edition of "Annals of Allergy, Asthma & Immunology," identified two proteins -- LTP and PG2A -- as major allergens in six common tomato varieties. Earlier research at Germany's Paul-Ehrlich-Institut, reported in the May 2004 edition of "Allergy," found that profilin protein in tomatoes strongly cross-reacted with proteins from other plant foods, and with birch pollen. Tomato ketchup may contain traces of these proteins, according to the U.S. Department of Agriculture's Nutrient Data Laboratory. Ketchup may also contain the food coloring tartrazine, a rare cause of hives and swelling.
Ketchup and mustard contain vinegar, and many brands have different spices. Other shared allergens may include sulfites and salicylates. Foods processed with vinegar often trigger allergic reactions in mold-sensitive people, according to the Cleveland Clinic website. The Cleveland Clinic also cautions against eating mustard and ketchup if you have salicylate sensitivity. Vinegar, tomato paste and dried spices all have high salicylate concentrations. Sulfite sensitivity may affect as many as one of every 100 people, advises the Cleveland Clinic. These common condiment preservatives may cause severe allergic reactions.
Allergic reactions to mustard and ketchup occur because the immune system misreads the condiments' proteins or other compounds as harmful organisms. It reacts by manufacturing immunoglobulin E antibodies to fight the compounds. The IgE antibodies trigger blood and mast cell release of histamines and other chemicals. Allergy symptoms follow the histamine release within a few minutes or hours after consumption. Mild reactions include hives, itching, nasal congestion and digestive distress. Severe symptoms include asthma and anaphylaxis, a life-threatening condition that may cause loss of consciousness. Anaphylaxis requires emergency medical treatment.
Management of mustard or ketchup allergy begins with diagnostic testing to determine which of the condiments' allergens cause the reaction. Avoiding mustard, ketchup and any other foods with those allergens prevents future symptoms. Oral or topical over-the-counter histamine medications control minor symptoms like itching and sneezing. People at risk of anaphylaxis should carry injectable epinephrine at all times.