What is mustard allergy?
Mustard allergy is a type of food allergy. Food allergy occurs when the immune system mistakenly identifies a food as harmful and releases chemicals such as histamine, causing symptoms
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What is mustard?
Mustard is a type of plant that belongs to the Brassica family, which includes broccoli, canola, cauliflower, cabbage, Brussel sprouts, and turnip. Since these plants are closely related to mustard, their seeds contain proteins that are very similar to the proteins in mustard seeds. Although data is limited, not all people with cross-reactivity to the seeds will have clinical symptoms. Cross-reactivity has also been demonstrated with the vegetables themselves.
Mustard plants have seeds that can be white, yellow, brown or black. The jars of mustard you see in supermarkets are made by grinding the seeds and mixing them with water, vinegar or other liquids. Different species are used to make different types of
mustard.
Other parts of the mustard plant can be eaten or used in foods, including:
• mustard leaves
• seeds
• sprouted mustard seeds
• flowers
• mustard oil
• mustard cress.
If you have a mustard allergy, these can all cause allergic reactions so it’s safest to avoid mustard in all its forms.
Mugwort-mustard allergy syndrome
If you have hay fever caused by allergy to mugwort pollen (a weed that causes late summer hayfever), you may react to mustard and other foods in the Brassica family. This is known as Mugwort-mustard allergy syndrome. It happens because mugwort pollen contains a protein that’s similar to proteins in mustard. This type of mustard allergy is not common in the UK.
What are the symptoms of mustard allergy?
The symptoms of mustard allergy usually come on quickly, within minutes of eating the food.
Mild to moderate symptoms may include:
- a red raised itchy rash (known as hives or urticaria) anywhere on the body
- swelling of the face, lips and/or eyes
- a tingling or itchy feeling in the mouth
- mild throat tightness
- stomach pain, vomiting or diarrhoea
More serious symptoms (anaphylaxis)
The term for this more serious reaction is anaphylaxis (pronounced ana-fil-ax-is).
Most healthcare professionals consider an allergic reaction to be anaphylaxis when it involves difficulty breathing or affects the heart rhythm or blood pressure. Any one or more of the ABC symptoms above may be present.
In extreme cases there could be a dramatic fall in blood pressure. The person may become weak and floppy and may have a sense of something terrible happening. Any of the ABC symptoms may lead to collapse and lack of consciousness and, on rare occasions, can be fatal.
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AIRWAY – swelling in the throat, tongue or upper airways, hoarse voice, difficulty swallowing -
BREATHING – sudden onset wheezing, breathing difficulty, noisy breathing, persistent cough
-
CIRCULATION – dizziness, feeling faint, sudden sleepiness, confusion, pale clammy skin, loss of consciousness or collapse
Getting a diagnosis
If you think you or your child may be allergic to mustard, see your GP. The GP can refer you to an allergy clinic if needed, or if a supervised food challenge is needed. They can find a clinic in your area from British Society for Allergy and Clinical Immunology (BSACI).
If you are referred, the consultant will discuss your medical history and symptoms with you. They might suggest skin prick tests, blood tests, and food challenge tests to help diagnose the allergy and work out how serious it may be.
What can mean you're at higher risk?
Some clues that you might be at higher risk of more serious reactions are:
- you have already had a serious reaction, with any of the ABC symptoms
- you have asthma, especially if it is not well controlled
- you have reacted to a tiny amount of mustard.
If you have asthma and it is not well controlled, this could make an allergic reaction worse. Make sure you discuss this with your GP or allergy specialist and take any prescribed medicines.
Treating symptoms
If you have mild allergic symptoms, you may be prescribed antihistamine medicine that you take by mouth. But if you are at risk of a serious allergic reaction (anaphylaxis), you may be prescribed adrenaline – the emergency medicine used to treat anaphylaxis. It is also known as epinephrine.
Because anaphylaxis can happen very quickly, adrenaline is available in different forms that are designed to be easy to use. It’s important to know exactly how and when to use your prescribed adrenaline. Healthcare professionals can show you how to use it, and there are also resources such as practice devices and videos on manufacturer websites.
Options currently available on prescription in the UK include:
- Adrenaline auto-injectors (AAIs) – EpiPen and Jext.
- Intranasal adrenaline – EURneffy, a needle-free nasal spray. (The 2 mg adult dose is available on prescription. A 1 mg dose for children weighing 15– 30 kg has been approved by the MHRA but is not yet available on prescription; it is expected to become available in Autumn 2026).
You must carry two in-date forms of prescribed adrenaline at all times as a second dose may be needed if symptoms do not improve after five minutes or get worse.
Avoiding mustard
Once you have been diagnosed with a mustard allergy, you will need to avoid mustard and foods that contain it.
Read the ingredient lists on food packets carefully every time you shop. Mustard is included in the list of top 14 major food allergens in the UK. This means it must be highlighted on ingredients labels, in bold for example.
Read the ingredient list every time you buy a product as manufacturers change their recipes often.
When eating out
Restaurants, cafes, hotels, takeaways and other catering businesses are required by law to provide information on major allergens, including mustard. Ask staff directly if the food you’d like to buy contains mustard and if there is a risk of cross-contamination and let them know that even small quantities can cause a reaction. Don’t be afraid to ask staff to check with the chef.
Which foods contain mustard?
Mustard can be used in a wide range of foods, for example:
- mayonnaise
- barbecue sauce
- fish paste
- ketchup
- tomato sauce
- marinades
- processed meats
- sausages
- piccalilli
- pickles
- pizza
- salad dressings and salad oil.
What else should I look out for?
- Mustard seeds and mustard oil are often used in multicultural cuisines e.g., Russian and Indian dishes.
- In Italian foods, look out for the word ‘mostarda,’. Mostarda is a sweet mustard flavoured preserve, often served with meat.
- The proteins in mustard that cause allergic reactions are not broken down by heat, so it can cause reactions even when it’s cooked.
- You may need to avoid the seeds and sprouted seeds of other members of the Brassica family. These might cause an allergic reaction as the proteins in the seeds are similar to those in mustard. This is called cross-reactivity. If you think you may also react to other seeds or plants in the Brassica family, let your allergy specialist know.
Key messages
- If you think you or your child may be allergic to mustard, visit your GP.
- If you are prescribed adrenaline, carry two devices with you at all times.
- Always be guided by your health professional on which foods to avoid.
- Ensure that asthma is well managed; see your GP if needed.
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