PATCH TESTING

Supplied by the Birmingham Skin Centre, City Hospital NHS Trust, Dudley Road, Birmingham, B18 7QU

What is patch testing?

Patch testing is a method for detecting allergies to chemicals which come into contact with the skin. The chemical may be found at work or in gloves, shoes, clothing, jewellery, hair dyes, cosmetics, perfumes, topical lotions or medicaments and numerous other sources in the environment.

Will patch testing detect all allergies?

No. Patch testing only detects one type of allergy. This is where a substance in contact with the skin causes an allergic skin rash. Allergy causing sneezing, sinus congestion, asthma or hives (urticaria) is detected by other techniques, for example scratch testing.

What should I bring to the patch test clinic?

Bring small quantities of substances which you are in contact with at work which you think may be causing or aggravating your rash. If possible try to find out their trade name, source of supply and chemical composition. Bring anything else which is coming into contact with your skin (e.g. cosmetics, lotions and creams, perfumes, topical medicaments and any other articles). All these items are needed on the first appointment. The doctor at the clinic will decide if you need Patch Testing to these items. If you are unable to bring samples, bring a list of all the materials involved and include all ointments involved in your treatment.

How may visits will be required?

Usually three. Patch tests are usually applied on the first visit, the results are read on the second and third visits. Occasionally a fourth visit may be required if extra patches are applied during the third visit.

How long will each visit take?

The first visit will be the longest. It usually takes an hour, sometimes longer depending on the number of patches applied. The second and third visits each last about 20 to 30 minutes

How are patch tests performed?

Suspected chemicals are applied in vertical rows on the back and covered with adhesive tape. The tape remains in place for 46 hours, and should be kept dry. Strenuous exertion (e.g. squash) should be avoided. The tests will be marked with a small amount of black ink. It is therefore a good idea not to wear a good bra, vest or shirt. The back has to remain dry throughout the duration of the testing.

Conclusion

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 skin condition. The medical staff will be pleased to answer any questions you have regarding the above during your hospital visit.