An abnormal reaction of the immune system to certain foods
Food allergy is a condition in which the immune system reacts in an inappropriate or exaggerated way to a specific food or foods, causing various symptoms such as an itchy, red rash and swelling of the lips, mouth, and throat. This condition should not be confused with food intolerance, which often causes abdominal discomfort and indigestion but does not involve the immune system.
Although allergic reactions can occur in response to any food, nuts (especially peanuts) are probably the most common cause. Other relatively common causes of food allergy include seafood, strawberries, and eggs. Food colourings and preservatives rarely cause reactions, but intolerance to the food additive monosodium glutamate (MSG) is common.
Wheat may cause a condition known as coeliac disease and an allergic reaction to the protein in cows’ milk is especially common in infants and young children (see Cows’ milk protein allergy). These conditions differ from immediate sensitivity to nuts or other foods in that they produce less severe but more persistent symptoms.
Symptoms may appear almost immediately after eating the food or develop over a few hours. They may include:
Itching and swelling affecting the lips, mouth, and throat.
An itchy, red rash anywhere on the body (see Urticaria).
Nausea, vomiting, and diarrhoea.
If you have a severe reaction, the following symptoms may also be present:
Nonitchy swelling anywhere on the body, especially the face, mouth, and throat (see Angioedema).
Shortness of breath or wheezing.
Sometimes, food allergy may lead to anaphylaxis, a life-threatening allergic response that causes sudden difficulty in breathing and collapse. If you develop the symptoms of a severe reaction, seek immediate medical help. If you develop anaphylaxis and have a syringe of injectable epinephrine (adrenaline), inject immediately, then call an ambulance.
You may be able to diagnose food allergy yourself if symptoms occur soon after eating a particular food, but you should consult your doctor, who may arrange for a blood test and skin prick test to find the cause. Your doctor may advise you to follow an exclusion diet, often for 1 or 2 weeks If your symptoms improve substantially while you are on the diet, this may indicate that you have one or more allergies to the excluded foods. You can then gradually add foods to the exclusion diet, but if symptoms recur when a particular food is introduced, you should avoid it. You should not embark on an exclusion diet without first consulting your doctor and you should not follow a restricted diet for more than 2 weeks.
Avoiding the problem food is the only effective treatment. Always ask about ingredients when eating out, and check labels. Consult a diet or nutrition counsellor if you need to exclude a food that is a major part of a normal diet. If a major permanent dietary change is needed, be sure to maintain a balanced diet.
Many food allergies in adults, particularly nut allergies, tend to be permanent, and people with such allergies must therefore avoid the relevant foods throughout their lives. However, in some cases, a food allergy may disappear spontaneously. Children under the age of 4 who avoid problem foods, such as wheat, for 2 years have an excellent chance of outgrowing their allergy.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.