Food allergy is a multi-system condition

Food allergy is a multi-system condition involving the immune system with reactions affecting one or more of three organ systems; the skin, respiratory system and/or gastrointestinal tract. The prevalence of food allergy is a reflection of the patterns of food consumption in respective countries around the world. For example, in the UK the most common food allergens are cow’s milk, egg, wheat and peanut and in China rice allergy is the most common.  Fish and shellfish allergy is more common in people of Asian decent, reflecting higher consumption in those countries.

Associated with atopic conditions such as asthma and eczema

It is however, universally associated with atopic conditions such as eczema, asthma, allergic rhinitis and hayfever, which run in families. An infant or child with a high risk of developing food allergy is one born into a family with one or more parent affected by an atopic condition, and stronger on the maternal line. The “allergic march” is the term which describes the multi-system response to development of atopic conditions in childhood.  In most cases, food allergic disease is outgrown in childhood, although there are persistent phenotypes which persist into adulthood.

atopic eczema

Courtesy of The Leap Study, Evangelina Hospital, London

Food hypersensitivity is an umbrella term

Food hypersensitivity is an umbrella term which describes food allergy and intolerance and is categorised and summarised in the table below. Importantly, differentiating between immediate (IgE) and delayed (Non-IgE) reactions is key to management and prognosis.

Classification of adverse reactions to food

Classification of adverse reactions to food

Immediate or delayed reactions?

IgE mediated reactions (usually immediate) occur within a few minutes of coming into contact with very small amounts of the offending food. Typically these reactions are more severe, typically involving the skin and/or respiratory system, and which take longer to outgrow. Diagnosis is usually made with allergy testing – positive skin prick testing and/or a specific IgE blood test, carried out in a hospital setting by a trained professional. Foods implicated in IgE food allergy including nuts, shellfish and wheat but also cow’s milk and egg.

Non-IgE mediated reactions occur anything from several hours to 3 days after consuming the offending food.   The reactions varying severity, usually from mild to moderate, less often severe, and typically involve the gastrointestinal tract. The length of time between food intake and reaction(s) make it more difficult to identify, however, non-IgE reactions do account for the majority of food allergic reactions in children today.   There is currently no diagnostic test to confirm non-IgE food allergy; foods implicated include cow’s milk, soya and egg.   Diagnosis is made with an allergy focused clinical history, dietary exclusion and controlled reintroduction, with clear written guidance from a trained professional.

Cow’s milk Allergy in Infancy

Infants consuming formula milk or who are symptomatic with mothers milk, and are suspected to have cow’s milk allergy, need paediatric dietetic support.  Importantly these issues should be addressed:  optimal nutritional intake including calcium, Vitamin D and iodine; the complete resolution of symptoms on dietary exclusion; attention to any associated feeding difficulties; education about individual prognosis and a plan for careful reintroduction of milk in a timely manner.  For more information see my blog series on Cow’s Milk Allergy in Infancy.