What is patch testing?
Patch testing can help your consultant dermatologist find out whether your skin condition is caused by an allergy to substances which come into contact with your skin, such as products at home, at work or in leisure activities. You can then be advised of the names of any identified allergens in order to help you to avoid them.
To what will I be tested?
You will be tested to at least 40 standard substances which are frequently in contact with the skin, eg. rubber, perfumes, preservatives, metals and plants, and also additional substances that are suspected triggers for your skin problem. You may be tested to some of your own work or home products, such as personal toiletries.
What does patch testing involve?
After your initial consultation and assessment with the consultant, three further planned visits to hospital during a single week are arranged.
On the first visit a specialist nurse will apply the tests to your back in special small containers contained within a tape. The containers are identified by marking your back with ink. Occasionally the arms or the thighs are also used. Itching of the sites is normal.
The substances remain taped in place until your next visit, when the patches containing them are removed and any reactions noted by the consultant. Additional patches may be added, as indicated by the initial patch test readings. Marking tapes are left in place.
On the third visit, your back will be examined by the consultant and any further reactions discussed with you.
Negative patch tests can still be helpful since, as far as possible, contact allergy as a cause of a skin problem will have been eliminated.
When can patch testing not take place?
You may not be patch tested if you are pregnant, breastfeeding, have extensive eczema on your back, have a suntan or have used a sunlamp over the previous two weeks, or are on a moderate or high dose of steroids. If you are planning to swim or take strenuous exercise, patch testing cannot be carried out as the patch tests will fall off.