Food allergy can be a complex, often, concerning condition, particularly in early childhood.

Food hypersensitivity is an umbrella term used to describe adverse reactions to food and includes food allergy, which involves the immune system, and food intolerances, which do not. Food hypersensitivity is used to describe objectively reproducible symptoms that are initiated by exposure to a defined stimulus at a dose tolerated by a normal person. Allergy is a hypersensitivity reaction that is initiated by specific immunological responses¹.

Food allergy is the largest single cause of food hypersensitivity in childhood and it can be further divided into IgE mediated (immediate) reactions or non-IgE mediated (delayed) reactions. Food allergy is common with data from a large birth cohort from Cork in 2014 reporting an incidence of 4.5% in Irish children with proven immediate food allergy (it is estimated that an additional 1-2% of children have delayed food allergy)². This is in keeping with an internationally reported prevalence of food allergy in children of between 5–10%.

It is important to distinguish food allergy, especially IgE mediated allergy, from other forms of food hypersensitivity because symptoms are replicated on subsequent exposures to that food and may, albeit rarely, cause severe or life-threatening reactions. A clear diagnosis of food allergy allows for the provision of appropriate dietary advice, the evaluation of future risks of exposure, and the delivery of appropriate treatment¹. Through careful and accurate diagnosis, this will aid in avoiding the use of unnecessarily restrictive diets which may negatively impact a child’s growth and quality of life.

Factors contributing to the development of food allergy include infections, antibiotic usage, mode of delivery, genetic, prenatal exposures, method of feeding, mother’s diet and health status, season and family structure.³

The diagnosis of food allergy is largely based on a detailed allergy focused history and examination. Emphasis should be placed on the importance of gathering a detailed allergy focused physical history for accurate diagnosis of a food allergy. IgE mediated (immediate) food allergy usually presents as a reaction which may involve the skin, respiratory, circulatory or gastrointestinal systems^1,4.

The timing of the onset of any of these symptoms is a crucial historical feature with immediate reactions occurring, usually within minutes but always within 2 hours of exposure. Urticarial rashes which are noted independent of food exposure (e.g. on waking) or that last for days are rarely due to food and usually have another cause such as a viral infection¹. Consistency is also important as true food allergy will always result in a reaction when there is repeated exposure to the same form of the food. For example, a parent who is concerned that their child is allergic to milk but who can eat regular dairy ice-cream without difficulty is unlikely to have a milk allergy.

Non-IgE mediated (delayed) food allergy occurs hours or days after exposure, typically within 2-72 hours. While there are certain well-defined cell mediated conditions such as eosinophillic proctitis (allergic inflammation of the lower bowel) in infants, most non-IgE mediated food allergy is non-specific and is usually considered amongst a long list of alternative diagnoses, especially in young children. A summary of the most common symptoms associated with both IgE and non-IgE mediated food allergy include the following^1,4:

Another key aspect of an allergy focused history is to identify the presence of predisposing factors, in particular eczema. Most children with food allergy have underlying eczema and most children with severe eczema will have food allergy⁵. Occasionally the eczema will have resolved by the time the child presents and this information will only be available from the history, further emphasising the importance of obtaining a detailed history. Milk allergy may present without a history of eczema. However, it is unusual to have egg or peanut allergy without a history of eczema. It is very important to assess the child’s nutritional status, noting weight, length and subcutaneous fat stores to aid in determining whether child is at risk of/is suffering with faltering growth.

Food allergy is often misdiagnosed, which can affect quality of life and increase the risk of faltering growth in this vulnerable population cohort. In practice, food allergy testing is currently only available for IgE mediated reactions. Confirming a diagnosis of food allergy is important as it justifies the avoidance of the suspect food allergen(s) and the implementation of an appropriate management plan. Conversely, a negative allergy test may allow for safe dietary expansion. Only when an individual demonstrates raised IgE to a food allergen (e.g. peanut) and reacts on contact with allergy symptoms, are they considered allergic¹. Many individuals have a raised specific IgE but will not react on contact with the allergen; these individuals have allergic sensitisation but not allergy. This is important in order to understand allergy testing as to indiscriminately measure specific IgE or SPTs will yield many people who are sensitised but not allergic (i.e. over-diagnosis).

In the case of non-IgE mediated food allergy there is currently no validated, reliable test apart from dietary exclusion and reintroduction. Because these reactions are generally mild (although troublesome) it is generally safe to reintroduce foods at home provided there is no evidence of IgE mediate allergy nor a history of a previous severe reaction.

It is important that practitioners have awareness of “alternative” allergy tests available to patients in the community, many of which are expensive. European and American allergy associations have recommended against using Vega testing, kinesiology and hair testing on the basis that there are no studies to support their use. They also advise against using IgG (as opposed to IgE) testing to foods as there is no validated evidence to support its use at this time.

Expert recommendation regarding the accurate diagnosis of a food allergy is illustrated below.

The management of food allergy will depend on the form and severity of the allergy, with appropriate support from healthcare professionals provide to parents and carers to ensure full nutritional requirements are met. For more in-depth guidance on the management of cow’s milk protein allergy (CMPA), please refer to the CMPA focused article on our website.