Food Allergy and Food Intolerance

If someone reacts to a food, they may have a Food Hypersensitivity (FHS). FHS reactions involving the immune system are known as food allergy (FA), all other reactions are classified as food intolerances (FI).

Food Allergy

Between 6-8% of children and up to 4% of adults suffer from a FA. People with FA develop antibodies against certain proteins in foods known as allergens. When they eat that food their body reacts, usually immediately or less than an hour after eating, although some babies can have very delayed reactions to milk. Reactions usually involve itching or swelling of the mouth/throat and itchy rashes and/or hives like insect bites. Wheezing, hay fever, eczema and flushing can also occur.

Symptoms can be severe and include life-threatening anaphylaxis. FA in adults is often linked to hay fever in the spring and/or summertime, with reactions. This condition is known as Oral Allergy Syndrome (OAS) and involves immediate symptoms, typically itching of the lips, mouth and ears, triggered by a cross-reaction between the pollen antibodies and plant food proteins.

Food Intolerance

FI is commonly reported; about 20% of the population alter their diet because they believe they have a reaction to food. However the numbers who actually have FI are likely to be much lower. FI does not involve the immune system; symptoms are usually less severe than those in FA and may occur hours or days after the food was eaten. The commonest type of FI is lactose intolerance which affects people who cannot produce enough of the enzyme required to digest milk sugar. FI may be linked to other conditions; about 70% of people with irritable bowel syndrome report symptoms to specific foods.

Foods Involved

The commonest foods causing FA are milk, egg, and peanuts, sesame seeds, kiwi fruit, fish, shellfish, tree nuts, wheat and soy. All of these foods (except for kiwi) have to be labelled if present or added to any food, however small the amount. A variety of fruits, vegetables or nuts can cause OAS, but the commonest triggers are apples, stone fruits (peaches, plums etc), hazelnuts and almonds. Milk and wheat are the foods most often reported to cause symptoms of FI.


FA and FI are best diagnosed by a specialist. For FA, tests measuring levels of food IgE antibodies may be useful, although a positive result may not mean the person is allergic to that food. There are currently no reliable tests to diagnose FI except when lactose intolerance is suspected. Once diagnosed, the only current treatment for FA or FI is avoidance of the known food trigger(s). Anyone with suspected or diagnosed FA or FI, who has cut out foods from their diet, needs to make sure their diet is not nutritionally unbalanced.

An expert assessment of the diet is essential for all children on food avoidance diets, and also for adults who are excluding milk or wheat. People with FA should also always carry their prescribed medication with them, and know when and how to take it. Some children will grow out of a FA, so teenage or young adults with an FA diagnosed in childhood should be reviewed.  

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