What is mustard allergy?

Mustard allergy is a type of food allergy. Food allergy occurs when the body’s immune system wrongly identifies a food as a threat. When this happens, the body releases chemicals, such as histamine, in response. It is the release of these chemicals that causes symptoms.

It’s not known how many people in the UK have a mustard allergy, but it’s thought to be rare. But if you do have a mustard allergy, reactions can sometimes be serious.

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What is mustard?

Mustard is a type of plant that belongs to the Brassica family, which includes cabbage, Brussels sprouts and broccoli. There are various species of mustard plant.

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 rash (known as hives or urticaria) anywhere on the body
  • a tingling or itchy feeling in the mouth
  • swelling of lips, face or eyes
  • stomach pain or vomiting.

More serious symptoms

The term for this more serious reaction is anaphylaxis (pronounced anna-fill-axis).

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.


More serious symptoms are often referred to as the ABC symptoms and can include:
  • right_arrow_orange_icon AIRWAY - swelling in the throat, tongue or upper airways (tightening of the throat, hoarse voice, difficulty swallowing).
  • right_arrow_orange_icon BREATHING - sudden onset wheezing, breathing difficulty, noisy breathing.
  • right_arrow_orange_icon CIRCULATION - dizziness, feeling faint, sudden sleepiness, tiredness, confusion, pale clammy skin, loss of consciousness.

Getting a diagnosis

If you think you may be allergic to mustard, see your GP who can refer you to a specialist allergy clinic if needed. They can find a clinic in your area from the British Society for Allergy and Clinical Immunology (BSACI).

It’s important to get a referral even if your symptoms were mild because it can be hard to tell if future allergic reactions could be more serious.

Once you get a referral, 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. If you are at higher risk of anaphylaxis, you may be prescribed adrenaline to use in an emergency.

Adrenaline comes in pre-loaded adrenaline auto-injectors (AAIs) that are designed to be easy to use. Make sure you know how and when to use them. Ask your healthcare professional to show you how to use your specific brand of AAI. You can also find help on the manufacturer’s website and get a free trainer device to practice with.

You must carry two AAIs with you at all times, as you may need to use a second one if your symptoms don’t improve after five minutes or get worse.

Adrenaline auto-injectors

The adrenaline auto-injectors prescribed in the UK are:

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 di Frutti is a sweet mustard syrup made with fruits, which is served as a relish to eat with meats.
  • 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 will 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

  • Visit your GP if you think you might have a mustard allergy.
  • If you are prescribed adrenaline auto-injectors (AAIs), carry them with you at all times.
  • Speak to your allergy specialist about which foods to avoid.
  • Read food labels carefully and ask staff about ingredients in restaurants, takeaways and cafes.
  • If you have asthma, make sure it’s well managed. See your GP about this.

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