Food allergy and intolerance The term food sensitivity is used to describe adverse reactions to food, but it's more commonly known as food allergy or food intolerance.

In this article

What's a food allergy? What's food intolerance? Who's affected?

Diagnosing sensitivity Food challenges Tips for managing food sensitivity

Medical review Anaphylactic shock

Our bodies have many defence systems to protect us from substances that could harm us. The job of the immune system is to recognise these substances and destroy them, and it does this by producing toxic chemicals and inflammation.

A true food allergy provokes an exaggerated and abnormal immune response, and this is caused by certain proteins in food.

If a protein provokes a specific increase in immunoglobulin E (IgE) in the body, the reaction can be severe, rapid and even life-threatening (see 'Anaphylactic shock' below). Symptoms include swelling of the mouth and throat, and breathing difficulties.

Other allergic reactions that increase immunoglobulins others than IgE tend to develop more slowly and cause symptoms such as eczema, diarrhoea or vomiting.

Peanuts are the most common food to cause severe IgE-mediated reactions. A more typical example of a non-IgE allergic reaction is one caused by cow's milk protein.

Reactions to food that don't cause the immune system to respond are known as food intolerance, and are caused by something in the food other than a protein. The symptoms of a food intolerance can be similar to a food allergy, but also include a whole range of other symptoms such as nausea or rashes. A food intolerance is rarely life-threatening in the way some food allergies can be. The symptoms tend to develop more slowly and require larger amounts of the food to cause the reaction.

Lactose intolerance is a typical example, where people who lack (or have low levels) of the enzyme lactase are unable to digest lactose properly. This results in symptoms such as bloating and diarrhoea.

Food sensitivity is thought to affect 1.5 to 3.5 per cent of adults and 2 to 8 per cent of children. Up to 90 per cent of food sensitivities are caused by just a few foods. These are:

• Celery
• Cereals containing gluten
• Crustaceans (such as crab and prawns)
• Eggs
• Fish
• Milk
• Molluscs (such as mussels and oysters)
• Mustard
• Nuts
• Peanuts
• Sesame seeds
• Soya
• Sulphur dioxide or sulphites

The most common foods that children react to are milk, peanuts, nuts, eggs, soya and wheat.

Children under the age of three are more likely to develop food allergies, but often these disappear as the child grows up. They're more likely to develop a food sensitivity if there's a family history of allergy.

The number of people who develop food sensitivities seems to be on the increase, but the exact reason for this is unclear. Factors such as genes, exposure to certain foods and the development of the immune system at birth are involved in determining whether someone develops a food sensitivity.