Patch testing

What is patch testing?

Patch testing is carried out over 3 short appointments to find out whether your skin condition is caused by an allergy to certain substances (called allergens).

The 3 hospital appointments will take place during 1 week and you must be able to attend all of these appointments.

Patch testing will help us to find out if you are allergic to anything that is coming into contact with your skin at work, home or in your leisure activities. Patch testing does not detect allergies related to diet, hay fever or asthma. You will be tested for your skin’s reaction to over 40 ‘standard’ substances which we find most commonly cause allergies. These include metals, perfumes, rubber, glues and preservatives which are found in many toiletries and creams. Depending on your skin problem, other patch tests may be applied.

Please note that it is not possible to apply test patches if

the skin on your back is scratched, sun burnt, has a rash or excessive hair growth. If you do have excessive hair on your back, please have the area shaved before your appointment.

Your 1st patch test visit: (Monday)

Allow 30 minutes for this visit. Please make sure that your back is clean, free of hair and that no moisturisers have been applied.

The substances we will be testing your reactions to will be put onto your upper back, and possibly arms, in the form of small discs on hypoallergenic tape and marked with ink. The patches stay in place for the next 48 hours. If a corner or edge of one of the patches becomes loose, please tape it back down (ask someone else to help you if you cannot reach). Itching of the patch test sites is normal and you may find your back movements feel a little restricted.

If you have an allergy to one or more of the substances, this will show up on your back even if the rash is elsewhere on your body. Once the patch tests have been applied you must keep your back dry until after the final appointment (Friday).

The image within the PDF below, shows the application of patches onto a patient’s back. There will be tape placed along the top of each patch. Patients who need more extensive testing will also have extra patches put onto their lower back or arms.

Your 2nd visit: (Wednesday)

Please allow up to 20 minutes for this appointment. The patch tests will be removed from your back.

We will look carefully at your skin and a first reading will be made. We may leave a strip of tape on your back, as this will help us identify any reactions that happen between Wednesday and Friday.

No results can be given at this stage. It is important that you continue to avoid getting your back wet as the substances will still be on your skin. This will allow us to see if you have any delayed reactions.

Your 3rd visit: (Friday)

Please allow 30 minutes for this appointment. The final patch test reading takes place on your 3rd visit and any skin reactions to the patch testing are recorded. The doctor will discuss the results with you and give you information about any of the substances that you have reacted to. This may help you to avoid contact with such allergens in the future.

Do I need to bring anything with me to clinic?

If your consultant wants you to be tested for products and chemicals used at your workplace, please bring in samples at least 2 weeks before your appointment. The samples should be in well-sealed, labelled containers.

You should also bring in the Health and Safety Data sheets which will be available in your place of work (you may need to speak to the Head of Health and Safety).

Can I carry on as normal when the tests are in place?

It is very important that you avoid getting your back wet during the whole week of patch testing.

You are advised to keep your back dry until after you have attended your final appointment. If the patches get wet, the adhesive tape may come off and the tests will be inaccurate. We recommend that you wash using a flannel during the patch testing week. If you feel you must have a shower, please direct the water onto the front of your body,

or take a very shallow bath and avoid getting your back wet.

During the patch testing week, we suggest that you wear old clothes as the pen and substances may mark or stain them. At bedtime wear nightclothes to stop the patches coming off. We also recommend that you avoid strenuous exercise or heavy physical work during the week. Sweating, bending and twisting movements may cause the patch test strips to come loose.

Be careful for the first 2 to 3 hours after the patch testing has been put onto your back, as this is when the patches are most likely to come off. If the patches come off, please contact the Dermatology Department for advice. The contact details are at the end of this page.

Some substances may stain the skin. This is normal and will wash off when the patch testing has been completed.

It is important not to expose your back to the sun or artificial sunlight (sun lamps) during the week of the patch testing.

Limits of patch testing

It is possible that your patch tests will be negative. This may be helpful in proving that contact allergy is not the cause of your skin problem. Usually, an allergic reaction shows when your skin becomes red and itchy at the test sites by the 3rd visit (Friday).

Sometimes, a reaction may develop after the patch testing has been completed. If this happens, please contact the Dermatology Department.

There are no other tests available which are as accurate as patch testing for finding out which specific allergens are causing your skin problems. It may be a single ingredient that is found in many different products.

When is patch testing not advisable?

Patch testing is not advisable if you:

• are pregnant
• are breastfeeding
• have extensive eczema on your back
• have been exposed to the sun
• have used a sun bed over the previous 2 weeks
• have recently applied an artificial tan

You should try to avoid using antihistamines for 48 hours before your 1st patch testing appointment and during the patch testing week as this would reduce any visible reaction to the allergens.

If you use corticosteroid creams on your back and upper arms, you should stop applying them 3 to 4 days before your patch testing begins.

Please let the dermatologist know if you are taking oral steroids as they may allow you to continue taking them during the tests. Moisturising creams should be stopped the day before the tests so that the patches can stick easily to your back.

Possible side effects

Side effects are rare, but include:

• Redness of the skin and itching at the application site (a positive test result) - this usually disappears after a few days. A strongly positive patch test may cause a blister
• Longer lasting positive reactions may be experienced for up to a month
• Flare-up of eczema - a positive patch test may be accompanied by a flare-up of existing or previous eczema
• Pigment change - an increase or decrease in skin colour may be seen at the site of the patch tests. This may last for months or rarely (1 in 1,000) be permanent
• Infection is rare but you would need antibiotic treatment if this happens
• Scarring - very rare (1 in 10,000)
• Allergy - rarely, in about 1 in 5,000 patch tests, you may become allergic to one of the substances applied

Cancellation of the appointments

If you need to cancel your appointments, please contact the Dermatology Department as soon as possible so that the appointments can be offered to another patient.

Contact information

If you have any questions or concerns, please contact the:

Dermatology Department

Gloucestershire Royal Hospital

Tel: 0300 422 8348 (answerphone)

Tel: 0300 422 8454

Please leave a message and someone will get back to you within 48 hours.

Further information

British Association of Dermatologists

Website: www.bad.org.uk/patient-information-leaflets

British Society for Cutaneous Allergy

Website: www.cutaneousallergy.org

Acknowledgement

Thank you to Bio-Diagnostics® for giving permission to use the image included in the PDF leaflet below.