Patch testing

This leaflet is not meant to replace the information discussed between you and your doctor, but can act as a starting point for such a discussion or as a useful reminder of the key points.

What is patch testing?

Patch testing is a test that can help your doctor determine whether your skin condition is caused by an allergy to substances, which have come in to contact with your skin either at home, at work, or during leisure activities.

To what will I be tested?

You will be tested to around 50 standard substances commonly in contact with the skin, such as rubber, chemicals, metals, perfumes, and plants, and also additional substances depending on your skin problem.

You may also be tested to some additional relevant substances, including those found at your work or home.

What should I bring to the Patch Test Clinic?

If you are an adult your first appointment will be a telephone appointment. If the appointment is for your child, there will be no telephone appointment and they will be seen by a doctor at their first appointment.

At this appointment your doctor will discuss the following with you.

• Any prescribed drugs you are taking.

• Ointments and creams you use including over the counter creams.

• Your own products, including substances you use at home which you think you might be allergic to, for example toiletries, cosmetics, nail polish, perfumes, and hair care products.

• Work chemicals, if you think that substances at work may be aggravating or causing your rash.

Your doctor will let you know if you need to bring anything with you for testing.

What does patch testing involve?

You will need to visit the hospital twice.

• On the first visit you will meet with the patch testing nurse. They will apply the substances to be tested in special patches to your back and the sites marked with ink. Each patch contains 10 allergens. Please allow up to one hour for this visit.

  These patches will remain in place for two days. After two days you remove them and mark with a special pen, as shown to you by the patch testing nurse. You then need to take a photo of your back to bring along to your second visit.

• At your second visit (on day four or five) your back will be checked and any reactions discussed with you by the doctor. Please allow 30 minutes for this visit.

What reactions could I have?

• 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 become obvious by your day four reading, although they can occasionally take longer.

• If you do develop a late reaction, please contact the clinic on telephone 01227 783167 or 01843 235058.

• Sometimes substances may stain your skin; this is normal.

Are there any reasons why I cannot have a patch test?

We may not patch test you if you:

• are pregnant or breastfeeding

• have extensive eczema on your back

• have had sun exposure or used a sun bed over the past two weeks; or

• are on a moderate or high dose of steroids.

If any of these apply to you, phone the clinic to rearrange your appointment.

What should I avoid before and during patch testing?

You should try to avoid antihistamines for 48 hours before your first appointment.

Do not:

• get your back wet during the tests; you can wash with a flannel

• wear your best clothes as the marker ink may stain; or

• expose your back to the sun during patch testing.

Do:

• avoid sport or heavy physical work during the week of your tests

• wear an old bra or t-shirt for the week of your tests and wear a t-shirt or vest to sleep, to protect the tests

• reinforce with tape if a patch peels off. If a whole patch comes loose remove and note the time and date.

  Contact us on telephone 01227 783167 if you are concerned.

What are the possible side effects?

Side effects are rare, but can include the following.

• Skin reddening and itching from positive test results; this usually disappears after a few days.

• Persistent reaction. Some positive test reactions for example to gold, may persist for up to a month.

• A positive patch test may result in a flare-up of existing or previous eczema.

• An increase or decrease in pigment may be seen at the site of the patch tests.

• Infection or scarring; these are rare.

• Sometimes you may become allergic to one of the substances used during patch testing. In practice this does not seem to cause a problem in the long-term. This can happen to around one in 500 patients.

References

You may find the following links useful.

• Chemotechnique Diagnostics patient video

• DermNet: patch tests

What if I have any questions or concerns?

If you have any concerns or need further information about your condition or the tests, please contact one of the following.

• Dermatology, Kent and Canterbury Hospital, Canterbury
  Telephone: 01227 783167

• Patch Testing Co-ordinator
  Telephone: 01843 235058