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What is a food allergy?

Clearing up the confusion

Allergy or Intolerance?

An allergic reaction is the body’s immune system responding to what would usually be considered a harmless substance, in an aggressive manner. The body perceives these substances as a ‘threat’ and produces an inappropriate response, which invokes symptoms. These symptoms usually start within a few minutes but can begin as late as two hours later. In contrast, a food intolerance is a difficulty digesting certain foods and experiencing physical symptoms as a result of eating them, with signs emerging hours to days 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 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 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 immune system protects us from diseases. 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 can provide you with results on many common allergens.

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.

Understanding allergies

It is essential to differentiate between an allergy and intolerance (or sensitivity). The classification of allergic and hypersensitivity diseases, which were defined by the European Academy of Allergy and Clinical Immunology (EAACI) and the World Allergy Organization (WAO) provides a clear 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 aetiology, meaning to be classified as allergic to an item there is a need for a positive test result as well as symptoms.

Allergies are the most common chronic disease throughout Europe. According to the EAACI, up to 20% of people with allergies struggle daily with the fear of a possible asthma attack or anaphylactic shock. It can be life-threatening.

There are a variety of environmental influences and genetic factors of the body, which underly 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. 

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

Allergies explained

For an allergy to exist, allergen sensitisation must first occur. Antigen-presenting cells, including macrophages and dendritic cells, are responsible for detecting the allergen. This can happen in a variety of ways, including inhalation via the nose and lungs, as well as through the skin and the gastrointestinal tract. 

When cells containing an antigen interact with an allergen, it is perceived to be an invader, even though we wouldn’t normally consider the substance harmful. Subsequently, the allergen is then absorbed into the antigen-presenting cell, processed and then displayed on the surface of the cell.

Next, the cell then migrates and presents the allergen. This process stimulates the B-cell and produces antibodies specific to the allergen. From here, these particular antibodies, (IgE) are then released and can 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 can 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 histamines and other mediators, all of which act differently and create a variety of symptoms in different organs.

The key to fully defining allergy pathogenesis and developing novel therapeutic possibilities may 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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