A patch test can help us find the cause of a possible allergic reaction on the skin. This reaction is called allergic contact dermatitis.
During patch testing, different substances are placed on the skin and taped in place. The patches are typically placed on the back, left on for 2 days and then removed.
Patch testing has been used for over one hundred years and is a method of detecting an allergy to a substance which has come into contact with your skin. These substances maybe found at work, at home or in leisure activities.
Patch tests detect the type of allergy which is due to direct skin contact with things outside the body. It does not detect allergies related to diet or inhalation which might produce sneezing, asthma or hives.
The substances to be tested will be applied in small containers to your back and the sites marked with ink. The patches are stuck on your back and do not involve any injections. The patches stay in place for two days and are removed on the second visit when initial results are taken. The sites may itch, this is normal. More patches may be put on your back at this stage.
It may be necessary to expose part of your back to ultraviolet light if we suspect a light-induced contact allergy (‘Photopatch testing’). The final results are read on the third visit and the doctor will talk to you about them. The second and third visits should take no longer than half an hour. It is advisable to bring a book.
Very occasionally the patches may be applied on the first visit, depending on the initial consultation findings.
It is possible that your patch tests will be negative. This is helpful since, as far as we can, we have eliminated contact allergy as a cause of your skin problem. Positive reactions become red and itchy at the test site and usually appear by the third reading, although they can occasionally take longer. If you do develop a late reaction, please contact us.
Sometimes substances may stain the skin, this is normal.
Before the tests
Please bring samples either in the original container or in screw top, airtight container clearly labelled to say what it is and your name.