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What is Food Allergy?

Food allergy is caused when the body mistakenly makes an antibody (IgE) to 'fight off' a specific food. When the food is next eaten (or sometimes is just in contact with the skin) it triggers an immune system response which results in the release of histamine and other substances in the body. These cause various symptoms, depending on where in the body they are released. For example, in the gut they may cause abdominal pain, vomiting and diarrhoea; in the skin, itching and swelling (rash or nettle rash); in the upper airways, a runny nose or sneezing; in the lower airways, a wheeze or cough. Very rarely the immune system chemicals are released throughout the body, causing a 'systemic' reaction (such as anaphylaxis).

Normally symptoms arise within a few minutes of eating the offending food, although they may be delayed by up to a couple of hours. The symptoms are usually those of 'classic' allergy such as rashes, wheezing, itching, severe gut symptoms or (very rarely) sudden collapse. The rapid onset of symptoms, which always occur in response to the same food, mean that most people will already recognize that the food causes them a problem. There are reliable blood tests (IgE or RAST tests) and skin tests, available through the NHS that can show quite accurately the presence or absence of food allergy.

The foods that most commonly cause allergy are milk and eggs, nuts (including peanuts) and seeds, shellfish, fish, wheat, soya and some fruits such as citrus and kiwi.

If a severe allergy has been identified, it is important that the sufferer should avoid even tiny amounts of their trigger food or substance. Very occasionally, reactions can occur even when the person has had skin contact with the offending food. For example, some peanut allergic people have suffered a severe reaction just through being kissed by someone who has eaten peanuts. A fish-allergic person may react by being in a kitchen where fish is being cooked.

As well as avoiding the offending food, the allergic person should be provided with appropriate emergency treatment should accidental exposure occur. Depending on the severity of reaction, this may be adrenaline to be given by injection, antihistamines, steroids, or all of these. The exact details of such treatment will need to be decided by the doctor in charge of the patient.

Individuals affected by severe food allergy should still be able to participate in all normal activities, school, work or leisure, but appropriate support and understanding is required.


There are 3 stages to managing a food allergy:

  1. Identify and avoid the cause (if possible)
  2. Recognize the symptoms of an allergic reaction
  3. Know what to do if it happens again

All people identified as having (or suspected of having) food allergy should therefore be referred to an allergy specialist in order to achieve this.

Additional strategies include:

  • Wear a 'Medic Alert' or similar bracelet or medallion
  • Inform work colleagues, catering staff, occupational health staff, teachers and first-aiders about your allergy.
  • Avoid the foods that cause your allergy totally - do NOT risk testing for the presence of your allergen (peanut, egg, milk) in food by eating a small amount - remember that tiny quantities of the allergen can cause a severe reaction.
  • Make sure you have an Allergy Management Plan, and tell others where it is. Keep a copy of it with any medications you have been given for an allergic reaction.
  • Take any medication prescribed for your reaction promptly if symptoms begin. Then call an ambulance or go to hospital immediately (do not travel alone).
  • If you have been prescribed an adrenaline auto-injector, carry it with you at all times. Make sure you know how and when to use it, and what other steps to take. Your family and colleagues should also know how and when to give your adrenaline, in case you become unable to give it yourself.

Other Food Reactions

A few people develop immune-system reactions to foods where the IgE 'allergy antibody' is not involved. They may develop 'contact' reactions to foods caused by immune system cell reactions, or by other, more unusual antibodies. The symptoms caused by these reactions are generally more delayed and less severe than IgE allergy reactions, but may lead to chronic symptoms in the gut (pain, diarrhoea, generalized unwellness), especially in children.


Last updated: March 2012