Patch testing is a test that can help your doctor determine whether your skin condition is caused by an allergy to substances in contact with your skin eg substances at home or at work.
If you think that you have an allergy as a cause of your skin condition, you will need to visit your GP who will refer you to the department. If you already have patch test appointments arranged, please read through the patch test clinic patient information leaflet.
Patch testing is an established investigation which has been used for over one hundred years. It 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.
Attending the clinic
The patch test (contact dermatitis) clinic is in the department of dermatology at The James Cook University Hospital, Marton Road, Middlesbrough. The clinic is on Monday morning, Wednesday morning and Friday morning. You will need to make three visits to the clinic.
After you have seen the doctor or specialist nurse on the first visit, a series of tests relevant to your problem will be prepared. This can take some time so please allow up to two hours for your first visit. You will be tested to around 40 standard substances commonly in contact with the skin, eg rubber, chemicals, metals, perfumes and plants, and also additional substances depending on your skin problem. You may be tested to some of your own work or home products and we may test you to trial allergens as part of the ongoing process of assessing new environmental allergies.
How is the testing done?
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 a fourth visit is required.
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 Friday reading, although they can occasionally take longer. If you do develop a late reaction, please contact the clinic. Sometimes substances may stain the skin, this is normal.
Before the tests
- If you have eczema on your back, the tests cannot be done.
- Do not sunbathe or use a sun lamp for two weeks.
- If you are taking steroid tablets we may not be able to do the tests.
When you come to the clinic please bring:
- A list of medication – any prescribed drugs you are taking.
- All creams and ointments you use, including over the counter creams.
- Small quantities of any item with which you are in contact either at home or at work and to which you maybe allergic eg make-up, cream, perfumes, gloves, shoes, plant leaves (with the name of the plant) etc.
Please bring samples either in the original container or in screw top, airtight container clearly labelled to say what it is and your name. Personal items will be returned to you after the tests.
If it is a chemical from your work please send health and safety data sheets at least two weeks before your visit stating your name, a day time telephone number and the date of your test.
Dr P Cousen
Department of dermatology
The James Cook University Hospital
If there are no data sheets the store man, foreman or factory manager should contact his supplier and ask for them to be provided. While we do not necessarily test all these substances we should like to see them and assess their relevance.
Attending work should not be a problem during the tests.
Do wear an old top and underwear as clothes might get stained.
Wear an old t-shirt or vest when sleeping to protect the tests.
Exercise that involves a lot of arm movements or sweating may cause the patches to fall off so avoid sport.
Use a non-allergenic tape such as micropore to stick down edges which become loose.
If you are taking anti-histamines these do not affect patch tests. However, if you are having additional skin prick tests you should let the doctor know.
Do not have a bath or shower.
Do not scratch any reactions.
Do not use a sun lamp or sunbathe.
It is advisable not to have these tests if you are pregnant or breastfeeding.
Patch testing is a continually developing form of investigation. Many new allergic substances are being detected every year. In order to determine the accuracy of these findings and improve diagnosis and treatment for our patients, we may need to test you to substances not specifically related to your condition.
Side effects are rare, but include:
- Skin reddening and itching from positive test results. This usually disappears after a few days.
- Persistent reaction, some positive test reactions, for example a reaction to gold may persist for up to a month
- Flare of eczema, a positive patch test may be accompanied by a flare of existing or previous eczema
- Pigmentary change, an increase or decrease in pigment may be seen at the site of patch tests
- Infection or scarring, these are rare
- Allergy, very rarely about 1 in 500 times, you may become allergic to one of the substances applied during patch testing. In practice this does not seem to cause a problem in the long term.
Storage of test results
We will record the information about your patch test results in a secure computerised database and will use the results for audit in accordance with good medical practice. Anomymised data may be used for research and shared with other centres.
If you see a reaction within three weeks of your visit to the clinic you must report it as it maybe important.
If you need to change your appointment please ring 01642 282570.