Mustard isn't always yellow and it isn't always a sauce
Once somebody has been diagnosed with mustard allergy, "avoid mustard" sounds like a reasonably straightforward instruction.
Until you ask what mustard actually means.
There is prepared mustard in jars and bottles.
There are whole mustard seeds.
There is ground mustard.
There is mustard powder and mustard flour.
There are mustard leaves and flowers.
There are sprouted mustard seeds.
There is mustard cress.
And there is mustard oil.
Current Anaphylaxis UK advice is straightforward: people diagnosed with mustard allergy should avoid mustard in all its forms.
That is the practical advice.
But the science underneath it is considerably more interesting, particularly when we reach oils.
To understand why, we need to return to something established right at the beginning of this guide.
Food allergy is principally about proteins.
And oil is principally fat.
Whole seeds present a deceptively obvious risk
A whole mustard seed seems easier to identify than mustard powder.
Sometimes it is.
Yellow, brown or black seeds may be clearly visible in pickles, chutneys, breads, salads or cooked dishes.
But whole seeds can also become surprisingly difficult to recognise in complex foods.
They can be small.
They can darken during cooking.
They can resemble other seeds or spices.
They may be incorporated into mixtures containing peppercorns, cumin, coriander or other seasonings.
And mustard seed is often used at an early stage of cooking.
In some South Asian cooking, for example, mustard seeds may be heated in oil until they crackle before other ingredients are added.
By the time the finished dish reaches the table, the diner sees a curry or vegetable dish.
The mustard entered the story twenty minutes earlier.
Again, visual inspection is a poor substitute for reliable ingredient information.
Powder and flour are easier to hide
Grinding mustard seed creates another problem.
A whole seed occupies a particular point in the food.
A powder disperses.
Mustard powder incorporated into seasoning can spread throughout a food so thoroughly that removing one visible component becomes impossible.
It can enter dry rubs, spice mixes, coatings, sauces, soups and processed products.
This is one reason powdered allergens can create significant cross-contact challenges in manufacturing.
A liquid spill generally goes downwards.
A fine powder can become airborne, settle on surfaces and travel with equipment or people.
Food factories handling powdered allergens therefore need to consider not only direct contact but movement through the production environment.
The consumer never sees any of that.
They see the final packet.
Which again demonstrates how much allergen safety depends upon processes happening far away from the person who eventually eats the food.
Mustard leaves are still mustard
Mustard leaves — often called mustard greens — are eaten as vegetables in numerous cuisines.
Someone familiar only with prepared British mustard might reasonably fail to associate a plate of leafy greens with the condiment in a jar.
But they come from mustard plants.
Current Anaphylaxis UK guidance includes mustard leaves, flowers, seeds, sprouted seeds, mustard oil and mustard cress among the forms somebody with mustard allergy should avoid.
This is an excellent example of why allergy education has to move beyond supermarket product names.
A food can change appearance completely while retaining its biological identity.
Mustard sprouts deserve special attention
A seed contains concentrated stores designed to support a new plant.
When germination begins, the biology changes dramatically.
Enzymes activate.
Stored nutrients are mobilised.
Proteins are broken down or newly produced as the seed becomes a young plant.
For somebody with mustard allergy, however, "sprouted" does not mean that the allergenic identity of the seed has safely disappeared.
Current UK guidance includes sprouted mustard seeds among the mustard forms to avoid.
It also raises an interesting issue involving sprouted seeds from other members of the Brassica family.
Because related plants can contain similar seed proteins, Anaphylaxis UK advises mustard-allergic people to avoid seeds and sprouted seeds of other Brassica-family plants and to discuss suspected reactions to related plants with their allergy specialist.
That advice is much more specific than saying:
"Avoid all cabbage-family vegetables."
And the distinction matters.