Food allergies: their causes and symptoms
A food allergy is an exaggerated immune response, triggered by proteins in certain foods. The most common type is caused by Immunoglobulin E (IgE), an antibody that releases several chemicals, including histamine. Histamine typically causes symptoms such as swelling of blood vessels and skin, itching, wheezing and excess mucus. Non-IgE-mediated food allergies can cause symptoms such as heartburn, indigestion and eczema. An allergy can be confirmed by a range of blood and skin tests and by an elimination diet.

In children, eggs, milk, soya, wheat and peanuts are the most common causes of allergy. Many children outgrow allergies to milk or eggs, but a peanut allergy is generally lifelong.In adults, the most common allergies are to certain fruit and vegetables, shellfish, tree nuts (eg, walnuts and almonds), peanuts and fish.

Current advice is to avoid giving babies allergenic foods before the age of six months. Where there is a family history of any allergy, babies should (where possible) be breastfed exclusively for the first six months.

A food allergy is not the same as a food intolerance, which can cause digestive symptoms such as bloating or pain, and which usually appears 12-36 hours after eating.

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By Cherill Hicks