The rise in the number of children with atopic (allergic) eczema has led to increasing interest in the role of diet in this condition. It is widely accepted that foods are among the many environmental factors that make this distressing skin disease worse. The strongest evidence to support this is the demonstration that children with atopic eczema respond well when certain foods are removed from their diet without their knowledge. Foods can also trigger eczema in adults that suffer from allergies.
What is meant by food allergy?
The term 'food allergy' is a much misused and misunderstood term. Any non-psychological, reproducible unpleasant reaction to a specific food or ingredient is known as a food intolerance. This is an umbrella term that includes food allergy and other reactions to foods (for example a deficiency of an enzyme required for digestion). Food allergy is a specific type of food intolerance that involves the abnormal reaction of an individual's immune system to common proteins in our food that are harmless to the majority of the population. As well as triggering skin conditions such as eczema, food allergies can also lead to symptoms such as a runny nose, respiratory problems (including asthma), dilation of blood vessels, flushing and difficulty in breathing. The severity of symptoms and discomfort varies but in a small number of people reactions can be life-threatening (anaphylaxis).
Which foods are most likely to cause an allergic reaction?
The most common triggers of food allergy are:
• Tree nuts
• Cows milk
• Fish and Shellfish
• Cereals containing gluten (including wheat, rye, barley)
• Some seeds (e.g. sesame seeds) can also trigger an allergic reaction. However, the foods most usually associated with eczema are fish, shellfish, eggs and nuts.
How is food allergy diagnosed?
Food allergy is extremely difficult to diagnose and, if suspected, expert advice from a GP should always be sought. It can be detected by skin tests using an extract containing the appropriate food protein (allergen) or by laboratory tests such as the RAST (radioallergosorbent) test. Confirmation of the existence of an allergy should be made by exclusion of the suspect food from the diet until symptoms subside followed by a challenge test with the suspected food, preferably without the knowledge of the patient or investigator. Such tests require medical supervision because of the risk of a severe reaction (anaphylaxis) that requires immediate treatment with adrenaline. When food allergy is incorrectly diagnosed, for example as a result of commercial laboratory tests of blood or hair, arduous and even nutritionally harmful diets may be prescribed for patients who do not have food allergies at all. The unnecessary avoidance of wheat can be particularly detrimental to health, as it is an important staple in the UK diet. The statutory fortification of flour in the UK makes wheat-based foods an important source of several minerals and vitamins including calcium, iron and B vitamins.
How is food allergy treated?
Once food allergy has been diagnosed, the food in all its forms needs to be eliminated from the diet. Suitable dietary advice is essential to ensure that a healthy, enjoyable and well balanced diet is maintained. This is particularly important for growing children who have high requirements for several nutrients.
Can anything be done to prevent allergies from developing?
There have been suggestions that breast-feeding may help to protect against eczema and other allergic symptoms. However, findings from various studies have been mixed except for infants whose close relatives suffer from allergy, when exclusive breast-feeding for 4-6 months does appear to provide some protection. There is no convincing evidence that avoiding allergenic foods during pregnancy and breast-feeding will reduce the risk of allergy from developing in infants unless there is a strong family history of allergy. In fact, restricting the growing baby's exposure to these foods may cause more harm than good, as it may be that the tiny amounts encountered via the mother are precisely the quantities required to trigger tolerance. However, as a precaution , it is suggested that peanuts or foods containing peanuts may be avoided during pregnancy and breast-feeding where a mother, father or sibling suffers from allergic disease and that infants are not given these foods until the age of 3 years.