Skin rashes can be caused or made worse by allergy. There are 2 common types of skin allergy.
Fast onset e.g. urticarial ( hives, wheals). These may be associated also with hayfever, asthma and sometimes gut symptoms. We can do both bloods tests and Skin Prick Tests for these.
Slower onset contact allergy (causing some eczema). These can be tested for with Skin Patch Tests.
Skin Prick Tests
In the prick test, a drop of the purified allergen is gently pricked on to the skin surface, usually the forearm. This test is usually done in order to identify allergies pet fur, dust, pollens, foods or dust mites. Results are interpretable within 15 minutes.
Patch Testing – Patient Information
Why is it Needed?
Patch tests are performed to find out if your rash is being caused by an allergy to a substance that comes into contact with your skin.
What Does it Involve?
The tests are painless and do not involve pricking the skin.
The patches are applied to your back in strips by the nurse. There are 60 items in 5 strips for the standard test. The doctor may have also suggested additional items. You will have been asked to bring in your own items as necessary. This first appointment takes about 30 minutes.
The patches are removed and any reactions on your back are noted by the nurse. Although the patches are removed, marks are left to show where each patch has been. This appointment takes about 10-20 minutes.
You will see the doctor who will examine your back for any positive reactions and you will be given appropriate advice. Please bring along any extra items for which you have been tested, as this may help to clarify the results of your patch tests.
What Preparations Are Needed?
During the 24 hours prior to your appointment please avoid oily baths and do not apply any creams or ointments to your back. This enables the tape to stick more firmly and prevents creams from altering the response to the test substances.
Patch tests cannot be carried out on sunburnt skin, so please do not sunbathe for at least a week before the test.
Keep the test patches dry. Your back must be kept dry until after your last appointment. Do not shower or bathe.
Avoid sport. Exercise involves a lot of movement and perspiration.
Peeling tapes. Please ask someone to check that the tapes are secure and in position. Should they start to peel at the edges they can be secured with tape such as Micropore.
Clothing. It is advisable to wear dark or older clothing during the test days as the skin marker pen may cause staining. Wear loose clothing overnight.
Expect some irritation. Sometimes irritation is a sign of a reaction taking place.
Avoid sunlight exposure to your back, as this may affect the test. This applies before, during and after testing until any positive reactions have subsided.
Work. In general this shouldn’t cause a problem. However if your job is very physical you may need to make alternative arrangements.
Are There Any Risks?
You may rarely become sensitised to the products applied. Occasionally you may have a reaction to the test tape or marker pen. Testing is not done if you are pregnant.
Possible Side Effects
Irritation to the area of testing.
Temporary redness to the adhesive tape used.
Eczema-like reaction to a positive item.
Itching, local swelling or small blisters at the test site.
A positive result means you are allergic to that substance and will need to avoid it in the future. Individual substance information sheets will be given.
A negative result means you have not reacted to those items applied. However, there are thousands of chemicals in the world to which you may be sensitive but which have not been tested for on this occasion.
Further Information can be found at dermnetnz