What is allergy?

Allergy is a general term that describes an abnormal immune response to a usually harmless substance.

Allergy occurs when the body’s immune system reacts to a substance in the environment that does not bother most people. Allergy involves inflammation that can be localised or affect the whole body depending on the extent of the immune response.

What is an allergen?

An allergen is a substance that is usually ingested, injected, absorbed or inhaled into the body, which the immune system recognises as a substance that may cause harm. These allergens stimulate a response from the immune system that presents itself as various forms of an allergic reaction, for example, hives, anaphylaxis and the exacerbation of allergic disorders such as asthma, eczema, and allergic rhinitis (hay fever).

What is an allergic reaction?

An allergic reaction is an immune system response to something that the body has identified as an allergen.

An allergic reaction can be life threatening, even fatal, depending on how the body reacts to the allergen.

There are two types of allergic reactions:

• an immediate response is when the body has an immediate reaction to an allergen, for example hives, tissue swelling, breathing difficulties, asthma or hay fever.
• a delayed response is where the immune response can result in such conditions as eczema, some forms of food allergy or contact dermatitis. These food allergies can often cause abdominal symptoms such as abdominal pain, vomiting, diarrhoea and gastroesophageal reflux. In some cases eczema may also occur.

Food intolerance

Food intolerances are different to food allergies, because they do not involve the immune system. The most common sort of food intolerance is lactose intolerance. Lactose intolerance means a person lacks an enzyme that is needed to digest milk. This affects the gastrointestinal tract and can lead to symptoms such as vomiting, diarrhoea, and abdominal pain after drinking milk or eating milk-containing products.

Food allergies

Food allergies in very young children occur mostly with milk products, egg and peanuts. Most food allergies resolve with age, however peanut allergy usually persists with age. Regular review with an allergist is vital.

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