When the immune system reacts negatively to a particular food, it results in a food allergy. Despite the food being safe, the body makes an allergic antibody against it. Strong mustard can irritate the tongue, mouth, and throat and cause the eyes to get wet. Rarely, some people may get allergic responses, including anaphylaxis, from any portion of the mustard plant. Anaphylaxis is a severe allergic reaction that could be fatal. "Sin a 1" is the primary allergen in yellow mustard, and "Bra j 1" is the primary allergen in brown mustard. Even if mustard is cooked in food, the enzymes don't degrade much in the digestive system, therefore, the allergen is still present.