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Food allergies

A food allergy is where your body reacts to certain foods. It’s often mild, but can be very serious for some people.

What is a food allergy?

A food allergy is caused when your immune system reacts to something you’ve eaten. Other non-immune reactions to foods may be described as intolerances or adverse reactions.

What are the symptoms of a food allergy?

Symptoms can affect different parts of the body at the same time and include:

  • Itchy feeling inside the mouth, throat or ears
  • A red itchy rash
  • Swelling of the face, or around the lips, eyes, tongue or roof of the mouth
  • Abdominal pain, nausea or vomiting

In serious cases someone may suffer from anaphylaxis, a severe allergic reaction where the airways or circulation are involved. Anaphylaxis starts suddenly and develops quickly. If you think someone is suffering from anaphylaxis call an ambulance immediately and check the person has their own Epipens which can be used.

Symptoms of anaphylaxis include any of the allergy symptoms above PLUS either symptoms of airway closure and/or drop in blood pressure:

  • Feeling lightheaded, faint or losing consciousness
  • Difficulty swallowing or breathing or wheezing

What causes a food allergy?

Food allergies happen when the immune system mistakes proteins in food as a threat and develops antibodies (immunoglobulin E; IgE) against those proteins. If you’re then exposed to the allergen, your body see the threat and releases a chemical called histamine. It’s this histamine that causes the symptoms.

The most common food allergies are:

  • Peanuts
  • Tree nuts
  • Some fruit and vegetables
  • Soy
  • Fish
  • Shellfish
  • Cow’s milk
  • Chicken eggs

People who suffer from a food allergy often also experience eczema, asthma or hay fever.

How is a food allergy diagnosed?

If you think that you may have a food allergy visit your GP. Your GP may refer you to a specialist.

You may be advised to get an allergy test. The most common is a skin prick test. This will involve stopping antihistamine tablets for 72 hours beforehand. During the test, your specialist allergy doctor will draw a grid on your arm and place a drop of liquid into each square.

Each liquid contains a different allergen. Your doctor will gently prick through the liquid into the top of the skin in each square. The allergens you’re allergic to will cause an itchy, red bump to appear within around 15 minutes. Those that you’re not allergic to won’t cause any reaction. You may then identify what to avoid.

Another way to determine your allergens is via a specific IgE blood test organised by your GP. Allergy specialists also have access to advanced molecular blood tests (component specific IgEs) that can differentiate between mild and serious types of food allergy.

When skin prick or specific IgE blood tests are negative (do not give any result) but a food is still suspected, an allergy specialist has access to more complex investigations. Firstly, you will be asked to bring in the actual suspect food for prick testing. This can be more accurate than using the liquid extracts. Secondly, if this is also negative, then you may be invited for a day case food challenge test where you eat increasing amounts of the suspect food under observation on a day case unit, with full medical cover and treatment facilities for anaphylaxis. This test is suitable for fit, healthy individuals where there is no other way to confirm the trigger.

How is a food allergy treated?

  • Exclusion is the mainstay of treatment – the foodstuff is removed from your diet. Depending on the complexity of this eg multiple food allergies or difficult to avoid foods eg nuts, you may be referred to a specialist allergy dietitian for further advice and support.
  • In cases of accidental exposure/ contamination , your specialist will issue a treatment plan. Depending on the severity this may include antihistamines +/- adrenaline autoinjectors (eg. Epi-pen) for anaphylaxis
  • If you have asthma, it is very important that your asthma is controlled as otherwise your allergic reaction to food may be much worse. Ask your specialist to check your asthma.
  • In adolescents and children, immunotherapy is now available via paediatric allergists for peanut allergy and some other foods. This approach is not available for adults at the moment.

If you’re unsure what treatment you should go for, or the above treatments don’t work for you, our team of expert specialists are here to help.

This content has been checked and approved by

Dr. F. Runa Ali  ›

Dr. F. Runa Ali is a highly experience Consultant in Allergy & Respiratory medicine at King Edward VII’s Hospital. Dr Ali set up King Edward VII’s Hospital first-ever dedicated Allergy clinic in 2009 and continues to work with allergy and respiratory patients on a regular bases.

Find your specialist in Food allergies at King Edward VII's Hospital

If you suspect you have a food allergy and you’re seeking an expert opinion, you can find the UK’s leading allergy specialists here at King Edward VII’s Hospital. Our consultants are hand-picked for you, making it easy to access the best possible care.

Dr. F. Runa Ali  ›
Special interests include:
Allergy medicine (+ 12) more
Miss Charlotte Foster  ›
Special interests include:
Oncology (+ 9) more

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