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What is a food allergy?

All the facts

Allergy or Intolerance?

An allergy is the body’s immune system responding to what would normally be considered a harmless substance such as pollen, food, mould, pets’ hair, insects, medicines or house dust mites. The body perceives this substance to be a ‘threat’ and produces an inappropriate response, with symptoms usually starting within a few minutes but also as long as two hours later. Whereas a food intolerance is a difficulty digesting certain foods and experiencing physical symptoms as a result of eating them, with symptoms emerging hours to days later.

Allergy = fast symptoms
Intolerance = symptoms emerging later

What is an allergy?

An allergy is a type I hypersensitivity meaning that exposure to an allergen results in the production of immunoglobulin E (IgE) antibodies, the release of histamine and symptoms. It is an immediate response known as an IgE-mediated immune response with symptoms occurring almost straight away, as soon as the offending item is ingested, inhaled or touched. Symptoms do not always happen immediately and can occur up to a couple of hours later.

Allergens are usually easy to identify due to the quick nature of the reaction within the body, however this does depend on the severity of reaction as well as other factors such as hydration, time of year and sometimes even the processing level of a food.

Many people know an allergic response to a food or non-food item has the potential to be life threatening in certain individuals. In the case of severe allergy even the tiniest traces of an allergen will have an effect on the body and will trigger an immune system response. This is because the immune system attacks a particular protein as though it could be a harmful pathogen.

Depending upon the type of item ingested and the individual, the symptoms will present themselves differently. They can appear in the form of skin rashes, hives, vomiting immediately after ingesting food, wheezing, coughing, nausea and even the swelling of mouth, throat and tongue. An individual with multiple allergies may also have different symptoms to different items.

When seeing these symptoms, it is so important that you know what to do, as an allergic reaction has the potential to be very serious. If diagnosed with food allergies, you must do your best to consistently avoid these items and in particular if you have severe allergies or asthma, so to avoid a potentially life-threatening situation. It is important to note that type I allergies are a lot less common than intolerances and sensitivities.

What is the difference between IgE & IgG4?

Our body’s defence system, the immune system, protects us from disease. Antibodies produced by the immune system are one method of protecting us from foreign bodies. They recognise and prevent bacteria and viruses from entering the body. The IgE class of these antibodies is responsible for allergic reactions. Lifelab IgE tests will provide you with results on certain allergies.

If you believe you have an allergy you will need an IgE test. If you believe you have an intolerance you will need an IgG4 test.

IgG4 subclass is the least abundant type of IgG antibody, and often needs building up. Intolerance reactions are usually subtler than IgE symptoms – and include headaches, nausea, stomach cramps, diarrhoea or constipation, fatigue, skin disorders and lethargy – but can cause long-term damage and chronic discomfort. Lifelab IgG4 tests will provide you with results for an intolerance.

Understanding allergies

It is important to differentiate between an allergy and an intolerance or sensitivity. The classification of allergic and hypersensitivity diseases, which were defined according to the European Academy of allergy and Clinical Immunology (EAACI) and the World Allergy Organization (WAO) is essential in providing a clarified definition.

According to the WAO, the correct diagnosis of an allergy is if specific conditions are met, including: a compatible clinical history, and positivity to in vivo and/or in vitro tests (IgE blood test or skin prick test) to prove underlying mechanism and etiology, meaning to be classified as allergic to an item there is a need for a positive test result as well as symptoms.

Living with an allergy is the most common chronic disease throughout Europe. According to the EAACI, up to 20% of patients with allergies struggle daily with the fear of a possible asthma attack or anaphylactic shock. It can be life threatening for certain individuals.

There are a variety of environmental influences and genetic factors of the host body, which underlie the immunopathogenesis of food allergy and its manifestations. There have been some clinical studies, which have altered many people’s understanding of what causes a food allergy. An example of this is the functional genetic variants in the IL-12 receptor b1, and the toll-like receptor 9, as these thymic stromal lymphopoietin genes and even IL-4 gene polymorphism have been associated with the increased risk of a hypersensitivity to certain foods.

Overall, food allergies are a chronic condition and can be hereditary. However, there has been a recent rise in women developing certain food allergies and allergic rhinitis during the menopause.

Allergies explained

In order for allergy to exist, allergen sensitisation must first occur. Antigen-presenting cells, including macrophages and dendritic cells are responsible for detecting the allergen. This can occur in a variety of ways, including inhalation into the nose and lungs, as well as through the skin and the gastrointestinal tract. When cells containing an antigen interact with an allergen, there is perceived to be an invader, even though this substance is not believed to be harmful on a normal basis. Subsequently, the allergen is then absorbed into the antigen-presenting cell, processed and then displayed on the surface of the cell.

What happens next is that the cell then migrates and presents the allergen, this process stimulates the B-cell, and produces antibodies specific to the allergen. From here, these specific antibodies, (IgE) are then released and are able to attach themselves to receptors on various surfaces of other cells in the mucosal surfaces and on subsequent basophils contained within the blood.

There is a period of sensitisation, and afterwards comes a period of latency, then on subsequent re-exposure to the allergen the allergic response is triggered. In this process an allergen is able to connect with the IgE on the surfaces of the mast cell, and this causes the cell to release nasty and inflammatory cell mediators. These include histamine and other mediators, all of which act differently and cause a variety of symptoms in different organs.

In order to fully define allergy pathogenesis and develop novel therapeutic possibilities, the key may well be in further understanding the gut microbiome and advancing research into epigenetics.

Prince, B.T; Mandel, M.J; Nadeau, K; Singh, A.M. Gut Microbiome and the Development of Food Allergy and Allergic Disease. Pediatric Clinics of North America. 2015;62:1479-92 Xie, J; Lotoski L.C; Chooniedass, R; et al. Elevated antigen-driven IL-9 responses are prominent in peanut allergic humans. PLoS One. 2012;7(10):e45377 Nursing Times. (2006). The pathophysiology of allergic responses.

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