Dermatology
Patch testing
Patient Information Leaflet
Introduction
This leaflet has been written to help you understand more about patch testing.
It tells you what a patch test is, what is involved and what the possible risks are.
What is patch testing?
It is a specialist procedure carried out by dermatology clinicians. It can help find out whether your skin condition is caused by an allergy to substances which come into contact with your skin. These are known as allergens, and can include products at home, at work or in leisure activities.
What are the benefits of the test?
The test will give you the names of any substances you are allergic to, so that you avoid them.
Which substances will be tested?
About 40 standard substances that are frequently in contact with the skin will be used in the test. These include rubber, preservatives, metals, perfumes and plants, and also other substances that are suspected triggers for your skin problem. The test may include substances requested by your hospital doctor or your personal toiletries.
The hospital doctor may ask you to bring certain products with you on your first patch test appointment.
What does patch testing involve?
You will need to visit the hospital three times in a week.
First visit
On the first visit, the substances to be tested will be applied to your back in special small containers held within a tape. The containers are identified by marking your back with ink and adhesive tape. Occasionally the arms or the thighs are also used.
If the area where the patch tests will be applied is hairy, we may need to clip the hairs using sterile surgical clippers. Do not shave the hair or remove the hair yourself, as this may cause a reaction.
The sites used will probably itch but we strongly advise you to try not to scratch them.
Allow up to 30 minutes for this first visit.
Please note that some substances may stain the skin – this is normal. The stains will wash off after a couple of days with showering or bathing.
Second visit
The patch tests containing the substances will need to be removed, and you will be assessed by a hospital doctor for any positive reactions.
The marking ink and tape will stay on your back and may be reinforced with the marking pen, to ensure it will last for another two days.
Third visit
On the third visit, the hospital doctor will examine your back again for any further reactions. These will be discussed with you by the hospital doctor. We will give you information leaflets about any specific allergies.
How will I know if I have a reaction?
Positive reactions become red and itchy at the test site. This usually happens by the third visit – the final reading. However, they can occasionally take longer, up to two weeks. If you do develop a late reaction, please contact the clinic on:
01384 244799 (9am to 5pm, Monday to Friday)
What if there are no skin reactions?
It is possible that your patch tests will be negative. This is helpful because, as far as possible, the test will show that contact allergies are not the cause of your skin problem.
What are the risks and side effects?
These are rare but include:
- Skin reddening and itching at the application site – this is a positive test result. This usually disappears after a few days. A strongly positive patch test may cause a blister.
- Longer lasting reaction – some positive test reactions, such as a reaction to gold, may last for up to a month.
- Flare of eczema – a positive patch test may be accompanied by a flare of current or previous eczema.
- Pigment change – an increase or decrease in pigment (colour) may be seen at the site of patch tests. This may last for months. Rarely it may be permanent (one person in 1,000 get this).
- Infection – this is rare and would need antibiotic treatment.
- Scarring – this is very rare (one person in 10,000 get this).
- Allergy – rarely, in about one in 5,000 patch tests, a person may become allergic to one of the substances applied during patch testing. However, this does not seem to cause problems in the long term.
What happens before the test?
You cannot have a patch test if you:
- Are pregnant or breastfeeding.
- Have a lot of eczema on your back – we may need to use another site for the test.
- Have a suntan, have applied an artificial suntan or have used a sunbed over the previous two weeks before the patch test.
- Are taking a moderate or high dose of steroid tablets. If you are not sure, ring us to check.
- Are taking immunosuppressive drugs in the form of tablets or medicine.
- Have taken antihistamine tablets or medicine over the previous seven days.
- Have used a steroid-based cream or ointment on your upper back over the previous seven days.
Therefore, if any of these apply to you, please telephone on
01384 244799 (9am to 5pm, Monday to Friday) to rearrange your appointment.
How do I care for my patch tests?
Do not:
- Get your back wet while the patch tests are in place (from bathing, swimming and showering). A cool shallow bath works well as long as you avoid the patch tests.
- Do not wash the area where patch tests have been applied until after your third visit to the department.
- Wear best or pale-coloured clothing as the marker ink may stain it permanently. Black clothing is recommended.
- Expose your back to the sun or artificial sunlight (sun lamps).
- Do any sport or heavy physical work during the week of the tests, as sweating could cause the patches to fall off.
Do:
- Do wear old clothing (including underwear) for the week of the tests, and wear an old shirt or vest to sleep in to protect the patches. To avoid moving the patches, clothes that open at the front can be easier to take on and off than those that go over your head.
- If a patch test starts to peel off, put medical tape over it to keep it in place. You can get this tape from most pharmacies. If a whole patch comes loose, remove it and note the time and date. Contact the Dermatology Department as soon as possible on 01384 244799 (9am to 5pm, Monday to Friday).
Can I find out more?
You can find out more from the following weblinks:
http://dermnetnz.org/procedures/patch-tests.html
Reference
This patient information leaflet was adapted from the British Association of Dermatologists’ patient information leaflet:
British Association of Dermatologists (2013) Patch testing. Available at:
If you have any questions, or if there is anything you do not understand about this leaflet, please contact:
Dermatology Department on 01384 244799 (9am to 5pm, Monday to Friday)
Russells Hall Hospital switchboard number: 01384 456111
If you have any feedback on this patient information leaflet, please email patient.information@dgh.nhs.uk
Originator: Lisa Hill. Date reviewed: October 2025. Review date: October 2028. Version: 3. DGH ref: DGH/PIL/01252