Immediate allergic reaction usually occurs within a window of 20 minutes to 2 hours after exposure to the trigger food. Immediate food allergies are driven by the IgE antibody which leads to release of histamine and other substances from allergy cells in the body. These may result in:
2. Pollen-food syndrome / Oral allergy syndrome
This is a milder form of immediate food allergy which usually occurs in later childhood in patients who are allergic to tree and grass pollens. Due to cross-reactivity between the proteins found in pollen, raw fruits and vegetables, these children can develop local allergic symptoms in the mouth and throat. These symptoms, however, do not usually lead to anaphylaxis.
Importantly, when fruits and vegetables are thoroughly cooked or processed they no longer cause oral allergy syndrome as the cross-reactive proteins are destroyed.
There are also delayed allergies which can result in eczema flares or problems in the gut such as colic, reflux, pain, loose mucousy and /or bloody stools and constipation. These delayed allergic reactions usually occur at least 2 hours after eating the food and may occur the following day(s) which makes diagnosis and management of this type of food allergy more difficult.
Management of food allergy is based on educating patients and their families on strict avoidance of the culprit food alongside the prompt treatment of allergic reactions, resulting from accidental exposure.
Dietetic advice, as part of a multidisciplinary consultation, has been shown to improve allergen avoidance with a resulting reduction in accidental allergen exposures in the community. Dietetic advice is also important in terms of ensuring adequate nutrition in children with food allergies and finding alternative foods for the child to eat.
Additionally, children and families are provided with a written personalised emergency management plan on how to recognise and treat allergic reactions. This plan should be shared with the child’s nursery or school and other persons who have responsibility for looking after the child.
The child’s emergency plan may include antihistamines alone. If the child has had previous anaphylaxis or has food allergy and asthma requiring regular medication, they will also require the provision of adrenaline auto injector devices and training on how to use them. As peanut and tree-nut allergies can be unpredictable, many children with peanut and tree-nut allergy are prescribed adrenaline auto injectors even if they have not had previous anaphylaxis and they do not have asthma.
Recent advances in allergy research have resulted in a more active approach to managing food allergy. These approaches include food allergy prevention by early dietary introduction of potentially allergenic foods, and inducing tolerance to known foods allergens.
Previously, the Department of Health recommended delaying the introduction of peanuts until the age of 3 years if there was a history of allergy in the family. This recommendation was based on limited data and has now been withdrawn.
Currently, Department of Health guidelines recommend exclusive breast-feeding until 6 months, complementary feeding ‘at around’ 6 months and avoidance of potentially allergenic foods (peanuts, tree-nuts, seeds, milk, eggs, wheat, fish or shellfish) until after 6 months of age. However, European and American infant guidelines recommend introducing complementary foods from 4 to 6 months of age.
There are several studies which have shown an association between earlier consumption of cow’s milk, egg and peanut and a reduction in allergies to these foods in childhood. These studies, however, do not demonstrate causation.
Results from two large interventional studies are now available, which can provide further clarity:
The LEAP study examined 640 children suffering with severe eczema or egg allergy between the ages of 4-11 months. These conditions put the children at greater risk of developing a peanut allergy.
The study focused upon two primary methods: firstly, a diet containing peanuts 3 times a week and secondly, complete avoidance of peanuts. Each child was randomly allocated one of these options and results were gathered to ascertain which approach might best prevent a peanut allergy developing. The final part of The LEAP Study commenced when the child reached 5 years of age, when each child was then fed a peanut to see whether it would induce an allergic reaction or not.
The EAT Study focused on 1303 children who were exclusively breastfed at 3 months of age. Each child was randomly assigned for either the introduction of six allergenic foods into their diet alongside the continuation of breastfeeding (cow’s milk, egg, wheat, sesame, fish and peanut) or avoidance of the aforementioned allergenic foods whilst breastfeeding until they were 6 months old.
The children were then assessed at the age of 3 years to see whether they are allergic to any of these foods.
Certain food allergies, such as cow’s milk, soya, egg and wheat, are usually outgrown after a few years of avoiding the food; however, fish, shellfish, peanut and tree nut allergy are not usually outgrown.
Food desensitisation (giving a child with a certain food allergy gradually increasing amounts of that food under close hospital supervision) for peanut, cow’s milk and egg shows considerable promise as a future form of active treatment but is not yet ready for routine clinical care. Importantly, food desensitisation does not cure food allergies as studies have shown that if the child stops eating the food for a few weeks the allergy returns in many cases. Desensitisation should not be tried outside hospital supervision as severe allergic reactions have been reported whilst undergoing this treatment.
Recent studies have shown that 70-75% of cow’s milk and egg allergic children can tolerate cow’s milk and egg respectively when it is extensively heated. This is because heating cow’s milk and egg denatures the allergenic proteins in these foods and thus allows some children to tolerate them. When possible, this not only improves the child’s diet and quality of life but has also been shown to accelerate the resolution of unheated cow’s milk and egg.
In two studies, children who incorporated baked milk into their diet were 16 times more likely to become tolerant to all forms of cow’s milk than children who avoided cow’s milk. Similarly, children who incorporated baked egg products into their diet were 14 times more likely to become tolerant to ordinary egg products, compared with children avoiding all forms of egg. Children regularly eating baked egg products also tolerated egg on average 2 to 2.5 years earlier. It is difficult to know which children can tolerate baked forms of cow’s milk and egg, as some children can have severe allergic reactions; even to baked forms of cow’s milk and egg. Thus this should only be considered after assessment by an allergy specialist, and should not be tried at home before assessment.
Research into food allergy prevention and tolerance induction has gained momentum in recent years. A more active approach to food allergy prevention and management is likely to result from this research in allergy centres around the world which will have many advantages for food allergic children and their families.