Food allergy

doi:10.1136/bmj.316.7140.1299

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Carsten Bindslev-Jensen

The public perceives food allergy differently from doctors—especially in relation to its symptoms and prevalence. In controlled scientific studies a low prevalence of food allergy has been found in British and Dutch adults, whereas the percentage of people perceiving their illness as being food dependent is much higher. The prevalence in adults, confirmed by double blind, placebo controlled food challenge, has been estimated to be 1.4%. This is in contrast to findings in children, in whom the overall prevalence of IgE mediated food allergies is 5-7%.

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Prevalence (%) of adverse reactions to foods in adults*

Definitions

Adverse reactions to foods may be classified as due to either true food allergy or non-allergic food intolerance. In contrast, food aversion refers to symptoms that are often non-specific and unconfirmed by double blind, placebo controlled food challenge.

Types of adverse reactions to foods

Food allergy due to IgE mediated mechanism (Coombs' classification, type I)
Food allergy not involving IgE, in which other immunological mechanisms are implicated (for example, type IV)
Non-allergic food intolerance (for example, pharmocological, metabolic, or toxic reactions to foods)
Food aversion (symptoms are often non-specific and unconfirmed by blinded food challenge)

A true food allergy is a disorder in which ingestion of a small amount of food elicits an abnormal immunologically mediated clinical response. Food may cause allergic reactions by several mechanisms. The classic type I, IgE mediated reaction is the most thoroughly studied and potentially important in view of the risk of life threatening reactions in some people. Evidence is increasing, however, for an important role for delayed reactions (classic type IV mediated reactions). For example, eczema in children may be exacerbated by milk ingestion, and a small proportion of adults with severe contact dermatitis due to nickel may react to nickel in their diet.

Common products containing preservatives

Non-allergic food intolerance may be due …