Hazard Identification

What is food allergy?

Food allergy can be defined as an adverse, immune-mediated reaction to food. Often, people will refer to any adverse reaction to food as an 'allergy.' However, it is important to remember that true food allergies involve the immune system and are almost invariably mediated through immunoglobulin E (IgE). The majority of food allergies are caused by proteins, which sensitise and then elicit an allergic reaction in sensitive individuals. Food allergy needs to be differentiated from food intolerance, a condition that has no immune system involvement and includes reactions to certain food components, such as lactose, amines and histamine. Adverse reactions that lack an immunological mechanism are sometimes referred to as non-allergic food hypersensitivity reactions. Food intolerances can sometimes be controlled by limiting the amount of a particular food eaten, but with food allergies, much stricter avoidance of the food is necessary. Only food allergy, and not food intolerance, can lead to the potentially fatal reaction of anaphylaxis.

Gluten intolerance or coeliac disease is also not to be confused with gluten or wheat allergy, even though the symptoms may be similar. Although coeliac disease is an immune system response, it is not mediated through immunoglobulin E, as all other true food allergies are. Unlike wheat allergy, coeliac disease is mediated through immunoglobulin A (IgA) and immunoglobulin G (IgG), and sufferers will develop gliadin-specific IgA and IgG antibodies. Coeliac disease does not cause the potentially fatal anaphylaxis associated with true food allergies if gluten is eaten.

Allergy-like food poisoning has also been confused, in some cases, with food allergy. The reaction occurs as a result of ingestion of histamine from products such as spoiled tuna, mackerel, other fish and occasionally cheese. Histamine is one of the primary mediators of allergic reactions and is released from the cells of the body during a true allergic reaction. In the case of allergy-like food poisoning, the histamine is ingested and then elicits the allergy-like symptoms.

Mechanism of Allergenicity

Immunoglobulins, such as IgE, are produced by the body's immune system as a defence against invading microorganisms. Sometimes, the body also mounts an IgE response against certain agents, such as pollen, dust, house mites and food, and it is this response that gives rise to allergic reactions such as hay fever and food allergy.

There are two stages to the development of IgE-mediated allergies. The first is the sensitisation stage, in which an individual on first exposure to an antigen (usually a protein) will undergo a series of metabolic reactions resulting in the production of specific IgE (an antibody normally only produced in response to parasitic infections such as malaria).

The second stage involves elicitation of an allergic reaction. IgE becomes associated with specific receptors on the surface of special blood cells packed with inflammatory mediators, such as histamine. On the next exposure to the specific antigen, the cell-bound IgE reacts with the antigen, causing the cells to release the inflammatory mediators, which then trigger the symptoms associated with the allergic response, such as difficulty in breathing, gastrointestinal upsets and skin itchiness, etc. These symptoms normally occur within a very short time following exposure to the antigen.

The majority of food allergens are proteins. Sensitisation can occur through ingestion of the allergen, or through inhalation of certain allergens such as birch or grass pollen. Owing to the similarities between certain allergens, cross-reactions can occur in some unfortunate individuals, who might find themselves allergic to more than one type of allergen. Cross reactions are particularly common between pollen or latex and some fruits and vegetables, giving rise to the syndrome known as pollen-fruit or latex-fruit syndrome.

Another sub-set of food allergies is known as 'exercise-induced allergy'. In this case, the allergic response occurs only when the specific food is eaten just before or after exercise.

Prevalence

The overall and worldwide prevalence of IgE-mediated food allergies is not precisely known. About 1-2% of adults and between 5 and 7% of children are believed to suffer from some type of food allergy, and it is believed that these numbers are increasing. The prevalence is higher amongst children who often grow out of allergies, such as cows' milk or egg allergy. Prevalence also depends on country, for example, peanut allergy is particularly common in the United States, where peanut butter is a very widely consumed food. Mustard allergy is particularly common in France, and celery allergy is very common in Switzerland, Germany and France.

Currently, legislation in the EU requires that the following allergens must be declared on food labels: cereals containing gluten, crustaceans, milk, eggs, fish, peanuts, soya beans, tree nuts, celery, mustard, sesame seeds and all their products, and sulphur dioxide. Legislation in the US requires that the following eight types of allergen be declared: cows' milk, eggs, peanuts, tree nuts, wheat, soya, fish and shellfish. (For more detail, please see Allergen Legislation).

This section of the Food Safety Hazard Guide covers the twelve major food allergens currently designated by EU legislation, although it is clear that allergies can be caused by many more foods than these.

Allergen nomenclature

An allergen is termed 'major' if it is recognised by IgE from at least 50% of a cohort of allergic individuals, but does not carry any connotation of allergenic strength; otherwise, allergens are termed 'minor'. The allergen designation is based on the Latin name of the species it originates from, and is made up of the first three letters of the genus followed by the first letter of the species finishing with an Arabic number, e.g Ara h 1 is an allergen from peanuts (Arachis hypogea), and Gly m 1 is an allergen from soya (Glycine max.).

Hazard Characterisation

Effects on health

The main symptoms of IgE-mediated food allergy
Gastrointestinal	Nausea, vomiting, abdominal cramping, diarrhoea
Respiratory	Wheezing, asthma, rhinitis
Cutaneous	Itching, urticaria (hives), eczema, atopic dermatitis, angioedema, rash.
Other	Hypertension, increased heart rate, tongue swelling, anaphylactic shock, oral allergy syndrome, laryngeal oedema

Dose-response

The amount of allergen required to elicit an allergic response varies tremendously between individuals and between allergens. In some cases, the dose required to elicit a response can be minute (measured in micrograms), and even kissing someone known to have eaten the allergen is sometimes enough to cause a reaction. Inhalation of vapours from cooking of the allergen can also cause life-threatening reactions for some individuals. For this reason, people with food allergies are generally advised to avoid the offending food completely.

Management of food allergy

Typically, the prevention of IgE-mediated food allergy involves avoidance of the offending food and strict observance of food labels. For management of specific food allergies, please refer to the relevant sections.

Sources of Further Information

Published

Bush R.K., Hefle S.L.
Food Allergens
Critical reviews in Food Science and Nutrition, 1996, 36, Suppl: S119-163.

On the web

IFST Information Statement Food Allergy
http://www.ifst.org/uploadedfiles/cms/store/ATTACHMENTS/allergy.pdf