An abnormal reaction to an ordinarily harmless substance or allergen. Commonly this can be due to food with the top allergenic foods being dairy, egg, soy, wheat, nuts, fish. Allergy to aeroallergens such as dustmite, grasses, pollen and pet dander trigger more allergic rhinitis (hayfever), asthma and other conditions.
A careful history and examination followed by appropriate testing if indicated, this could be in the form of a blood test or skin prick test (these tests cannot be interpreted in isolation and must be directed by a clear history and examination to enable interpretation).
Skin Prick Test (SPT)
A painless procedure where a tiny amount of the allergen is placed on the skin and left for 15 minutes before it is read for a reaction. Cannot be done if anti-histamines are being taken.
Link to SPT information sheet
Blood test (RAST)
More invasive than a SPT, not affected by antihistamines, sometimes needed as well as SPT to determine the nature of an allergy.
Not all substances that cause allergy can be tested for.
This is an abnormal reaction to a food that is not due to the immune system causing an allergy. The diagnosis is made with careful history, sometimes a food diary or removal of the food and re-challenge under careful supervision.