Mustard allergy is quite rare in the UK, but it is more common in other European countries, such as France, where it has been reported to cause severe reactions, including anaphylaxis.
People who are allergic to mustard will react to any food that comes from the mustard plant, including jars of mustard, mustard powder, mustard leaves, seeds and flowers, sprouted mustard seeds, mustard oil, and foods that contain these.
Since November 2005, food labelling rules require pre-packed food sold in the UK or the rest of the European Union (EU) to show clearly on the label if it contains mustard (or if one of its ingredients contains it). Bear in mind that there could still be foods on the shelves that were produced before this date.
Traditional mustard and cress contains seedlings grown from mustard seeds and because it generally isn't pre-packed, it wouldn't have to be labelled as containing mustard. But much of what is sold as 'cress' in the UK comes from other plants and doesn't include any mustard.
