To diagnose contact allergy a patch test is used. The test is done either at a specialist dermatology clinic or at one of the dermatology departments at the university hospitals.
The patch test
When a patch test is done the person is tested with a small amount of the allergen that is suspected of causing the eczema. The allergens tested are in small foil pockets, or patches, on an adhesive strip, and is attached to the back for 48 hours. The dermatologist removes the strip to see if there is an allergic reaction on the skin under where the specific allergen was placed.
A multi-substance test
The patch test usually tests a person's reaction to about 30 allergens. This is in accordance with the European standard series recommended by European dermotologists.
The standard series includes metals, such as nickel, chromium and cobalt, latex, perfumes, preservatives, colouring agents, plant extracts and pharmaceuticals.
In most cases the European standard series is not sufficiently broad to give a precise diagnosis, and supplementary tests with selected substances are often necessary, depending on the patient's occupation and particular symptoms. For instance, specific cosmetics, work gloves or shoes may be tested additionally.
Looking at ingredients
If the results of the patch test are positive, the dermatologist follows this up with a detailed investigation into the patient’s health to find out when and where the first contact with the allergen took place.
Sometimes it is necessary to look into the list of ingredients on cosmetics and cleaning agents and products used in the workplace; and to make further tests or chemical analyses of the various products.
Not always an answer
This is how any environmental causes of the eczema can be pinpointed. Knowing what these causes are plays an important role in preventing any new flare-ups or worsening of the eczema. Nevertheless, it is a difficult process and one that does not always lead to an explanation.
Even if an allergy is proven, the patient may have acquired it long ago, and it may not even be related to the current eczema. But knowing about an allergy is important to minmise the risk of developing eczema through exposure to the particular allergen.
It may have been many years since the patient was exposed to the allergen and it is no longer a direct cause of the current eczema. An example of this is nickel allergy, which often occurs in puberty as a result of teenagers tending to wear inexpensive jewellery containing nickel.
