Mustard condiment is prepared from mustard seeds. It is widely used in numerous kinds of seasonings and sauces as well as in other industrial preparations and can often arise as a masked allergen leading to serious allergic reactions. Mustard seeds are classified in Brassicaceae (Cruciferae): Sinapis alba and Brassica juncea varieties are used for food products. Brassica nigra seeds have been used in pharmaceutical industry for cataplasms, because of their revulsive properties. All species of cabbage and rapeseed belong to the same family, as well as turnip, radish, horseradish, rutabaga, watercress and another kind of lettuce: Eruca sativa.
The processed foods which may contain the raw material are pickled gherkins, and small white onions, often mixed with natural seeds. Various spicy sauces, vinaigrettes, mayonnaises often contain mustard condiment. Mustard is also used as an ingredient in many ready-cooked dishes, fritters, crackers, appetizers, various flours marketed for pizzas, fritters, dehydrated products for soups. Mustard is even present in baby food. It is a contaminant of hot-dogs (even without mustard), simply because of the salesmen's handling them. The risk of contamination cannot be excluded for fast foods restaurants (advice for avoidance may be consulted on website www.cicbaa.com).
The symptoms are those of every food allergy to potent food allergens: anaphylactic shock, exercise-induced anaphylaxis, serious systemic reactions of immediate type (urticaria, angioedema, asthma), rhinitis, atopic dermatitis in children, abdominal pain and diarrhoea, contact dermatitis in salad makers, contact urticaria for workers in food factories.
The frequency of anaphylactic shock noted in clinical reports points to the seriousness of allergy to mustard. No fatalities have been recorded. The patients, whether man or woman, often have associated sensitizations to pollens and other food allergies as well. Sensitization to Brassicaceae pollens (mustard or rapeseed pollens) should be analysed in patients suffering from rhinitis.
How much is too much?
The routine consumption of mustard condiment has been evaluated to 1340 mg. In a study using double blind placebo - controlled oral challenges, out of 28 children and two adults, two patients reacted to 40 mg and 440 mg, and six subjects reacted to 1340 mg. Reactive doses of mustard allergens may be very low, since the seasonings contain about 33 % of seeds, the protein equivalent being 6 % of the condiment.
Related foods (cross reactivity)
Cross-reactions have been rarely reported. Historically, the use of cataplasms was shown to induce allergy to mustard, documenting the reality of sensitization to food proteins by skin application. Single cases have been described of cross allergy to cauliflower, broccoli, coleslaw, cabbage, or to Brazil nuts, probably linked to similar allergens. A marked common reactivity has been shown between mustard and the major allergen of rapeseed. Colza-seeds have recently been introduced in appetizers; the use of colza-flour in vegetarian burgers is on the increase in the USA and is soon to be found in Europe: This should be kept in mind as they could change the situation. In two cases a mustard allergy occurred in patients sensitized to inhaled isocyanates, raising the hypothesis of a cross reaction with isothiocyanates of mustard seeds, but this still needs to be confirmed.
Who, when, how long, and how often?
The habits of consumption seem to differ in various countries. Data about the prevalence of mustard allergy is provided mainly by French authors. The relative prevalence of mustard allergy in France may be expected since France is the largest producer and consumer of mustard. Regional differences are observed: 0.8% to 1% of food allergies are due to mustard in the East part of France, 3% in the centre of France, 8.9% in the South of France, 1.5% in Spain. Cases might be quite frequent in Spain as well as in India.
Diagnostic procedures currently use prick-tests to mustard seeds or even to the condiment with similar results. The detection of allergy antibodies can easily be performed in blood samples. However as for many other foods, there is a clear discrepancy between the frequency of reactions evidenced by skin tests or blood samples, and a real food allergy. Only 23% of subjects reacting to mustard in diagnostic tests are able to react to the ingestion. Neither the size of the prick-test nor the level of allergy antibodies is predictive of a clinical reaction. Therefore, when tests are not conclusive, standardized oral challenges can be carried out in hospital settings. The diagnosis of allergy to mustard (and other spices) should be systematically considered in every case of immediate reactions after meals, where there is a strong suspicion of a food allergy, but where testing of all the common foods does not give a positive result. Also cases of unexplained anaphylaxis (so-called idiopathic anaphylaxis) could benefit from such investigations. Challenge of the lips is of no use, since there is an irritative, non specific effect of mustard on the lip. An alternative diagnosis of intolerance to sulfites has to be considered, since sulfites are commonly included in mustard seasoning itself.
Dietary precautions are mandatory: Extreme caution is recommended since the important allergen possesses a high resistance to digestion in the stomach, since mustard is often a masked allergen in many foods prepared by alimentary industries, and finally because the threshold of reactivity is low (advice for avoidance may be consulted on website www.cicbaa.com).
The modified directive of the European Community published in November 2003 takes these considerations into account and labelling of "mustard and products thereof" is expected to be implemented in 2004. Such compulsory labelling will prove all the more useful as the consumption of mustard is bound to increase with the spreading of industrially-made food aliments throughout Europe. Patients will be advised to have a close look at the labels.