A food allergy is when the body’s immune system has an abnormal reaction to certain foods which it sees as being harmful.  Most allergic reactions are mild, but sometimes they can be life threatening or fatal.

With food allergies the body’s immune system overreacts to an allergen.  These allergens aren’t usually harmful and most people are not sensitive to these allergens.

The ability to have a food allergy is an inherited predisposition.  If you have a family history of allergies (food, asthma, hay fever etc.), you are more likely to develop a food allergy.    For children with two allergic parents the risk of developing an allergy is much higher compared to a child with non allergic parents.  The presence of other allergic reactions or conditions i.e. eczema or asthma, can increase the likelihood to develop a food allergy.   Although food allergies are more common in children than in adults, most children grow out of allergies as they get older.

Sensitisation happens with the first time a certain food e.g. nuts is eaten, the body does not react and no symptoms will be experienced.   Once the same food is eaten again, the body is able to identify the allergen as an invader and it will start producing antibodies and release histamine; causing a range of symptoms to deal with the culprit.

In the case of a single food allergy diagnosed, it may also be possible to react to other similar foods; this is called cross-reactivity e.g. with a shrimp allergy, crab, lobster and other shell fish can also cause an allergic reaction.

Types of food allergies

Most food allergy sufferers will have IgE (immunoglobulin E) mediated allergic responses; which is due to an antibody reaction by the body’s immune system.

The other type is non-IgE mediated food allergies, but in this case symptoms develop over several hours or days after eating the culprit food.  The symptoms (eczema or diarrhoea) from non-IgE mediated allergies usually last longer than those caused by IgE mediated responses.

Food allergies must not be confused with food intolerances.  Although food intolerances can have similar symptoms to a food allergy, these do not involve the immune system.  Lactose intolerance is a common example; symptoms may include abdominal cramps, bloating and diarrhoea


The symptoms experienced during an allergic reaction will depend on where in the body the chemicals and antibodies are released.

Symptoms usually develop within a few minutes to two hours of eating or touching the culprit food.

Mild symptoms include;

  • Itchy or swollen lips, mouth, tongue or throat
  • Rashes, hives, eczema or flushed skin
  • A runny or blocked nose
  • Sore, red, itchy eyes
  • Diarrhoea, blood in stools, abdominal cramps and bloating (especially in infants and young children when allergic to milk and soy)
  • Nausea

An anaphylactic reaction is a severe whole body reaction to an allergen.  As well as the symptoms listed above, more serious symptoms can also be present or develop suddenly. More serious symptoms include; trouble breathing, wheezing and a loss of consciousness.  Although anaphylaxis is rare it is vital to seek immediate medical help.

Culprits causing food allergies

Any food could potentially cause an allergic reaction, but 90% of all food-allergies are caused by eight foods;

  • Milk
  • Eggs
  • Soy
  • Peanuts
  • Wheat
  • Tree nuts (brazils, almonds, cashews, hazelnuts, walnuts and pecans)
  • Fish and shellfish.

Milk and soy allergies remain the most common ones diagnosed in infants and young children; this is mostly due to the immaturity of their digestive systems.

Children can sometimes outgrow their food allergies especially if they are allergic to milk, eggs or soy.  Where peanut, fish or shellfish allergies are not usually outgrown.

It is very important to identify allergens and avoid the culprit foods as an allergy can in some cases be life-threatening or fatal.

Diagnosis of a food allergy

Your doctor will ask about the symptoms experienced, how soon these develop and take a medical and family history.  If a food allergy is suspected, a referral will be made to a specialist.

Main allergy tests include:

  • Skin prick tests – A small and diluted amount of the allergen is put onto the skin and a small scratch is made through it.  A positive result will be when the skin becomes red and swollen.
  • Elimination diets – Stop eating and avoiding the possible culprit food to determine if the symptoms improve.
  • Blood tests – RAST tests measure the amount of antibodies in the blood to a suspected allergen.
  • Food challenges – given a small amount of the culprit food to see what happens.  These tests should only be done in a hospital or clinic.

Treatment of a food allergy

Most allergic reactions are mild and many children outgrow their food allergies.  Although there is no cure for a food allergy, they can be prevented by avoiding the culprit food(s).

Ask your doctor to refer you to a dietitian who can show you how to identify problem foods and ensure that a healthy, balanced diet is still followed.

Some pregnant women follow a restricted diet in the hope to avoid allergies in their babies, but this is not recommended unless the mother (or father) has a food allergy or if there is a strong history of food allergies in the family.

Whilst exclusive breastfeeding, the mother should follow an exclusion diet to avoid the food her baby has an allergy to.   Once weaning is started ask your dietitian’s help to ensure you are eliminating the culprit and possible cross-reaction foods from your baby’s diet.

Some tips that may be helpful;

  • Check all food ingredient labels
  • Take care when cooking at home – do not contaminate food with any possible allergens.
  • When eating out, carefully read menus and as inform the staff about your food allergy.
  • Take care when buying pre-packed foods (bakeries, coffee shop, deli etc), these do not always have ingredients listed.

Bianca Parau, Senior Paediatric Dietitian, 
Bupa Cromwell Hospital, Cromwell Road, London, SW5 0TU

T: 020 7460 5566 | F: 020 7835 2518 | E: bianca.parau@cromwellhospital.com


About The Author

Paediatric Dietitian

Bianca is an experienced Paediatric Dietitian offering expert advice and guidance to children and their families with a friendly yet professional approach. After graduating from the University of the Free State she started her career in South-Africa. Since relocating to the United Kingdom she's worked at various top NHS hospitals as well as private health care centres across the country. She offers private appointments in her London and Home-counties clinics. Her current NHS clinical role at Chelsea and Westminster Hospital includes a multidisciplinary feeding clinic. With 16 years’ experience, Bianca is passionate about helping children of all ages to develop a healthy attitude towards food whilst meeting their nutritional requirements to sustain optimal growth and development. She works closely with paediatricians, paediatric allergists, paediatric gastroenterologist and various paediatric allied health professionals to provide comprehensive multidisciplinary evidenced based treatment. In addition to her private practice and NHS role, Bianca does consultancy work; she is a spokesperson on nutrition related topics and writes peer reviews as well as articles for various publications. Bianca is registered with the HPC-UK and is a full member of the British Dietetic Association.

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