Patch Testing

Download and print as a PDF (241kB pdf)

What is this information about?

This information is about patch testing. It explains:

• what a patch test is and what the results can tell us 
• when you will have patch test appointments 
• how to get ready for your appointments 
• what happens during a patch test 
• what you need to do during and after the patch test to make sure that the patch test works as well as it can look after yourself.

Why have I been given this information?

You have been given this information because you have been sent (referred) by a doctor or specialist nurse to have a patch test.  

This information will help you to know what to expect from your appointments and having a patch test.  

Following the advice and instructions in this information helps to make sure your patch test works as well as it can. This means we can use the results to find out what you are allergic to and to help you to manage your allergy in the best way.

What is patch testing?

Patch testing is done to find out whether there are certain allergens that cause your skin condition or aggravate it (makes it flare up). It will also test whether you are allergic to substances that touch your skin.  

Allergens are substances that can trigger an allergic reaction. We test for allergies to around 50 things that can often come into contact with skin. These include nickel, preservatives, cosmetics, perfumes, and rubber.  

Your skin may come into contact with an allergen at home, work or when you are out and about doing things such as sport or a hobby.

Be aware, patch testing does not:

• test for food allergies 
• test for allergies to things that you breathe in (inhale) such as pollen 
• find out which things irritate your skin

Skin irritation is not the same as having an allergy. Some things can irritate your skin without your immune system trying to fight them with an allergic reaction. For example, you can get ‘contact irritant eczema’ from your skin coming into contact with things such as cleaning products, acids, cement, antiseptics, soil and some plants.

What things can the patch test identify that I may be allergic to?

• You will be tested for an allergy to around 50 substances that commonly come in contact with the skin, including nickel, preservatives found in creams and shampoos, perfumes and rubbers (see pages at the end of this leaflet for full list of allergens).
• You may be tested for an allergy to some products that you use such as moisturizer or make-up. We do not test for products which you put on your skin but are then diluted (watered down). Shampoo is an example of this type of product as it is diluted when you wash your hair.

What must I do, and not do, before my appointment?

What should I bring to the patch test clinic?

On your first appointment please bring:

• A list of any medicines that you are taking. This should include medicines that you have prescribed and any that you have bought from a pharmacy or supermarket. 
• Any of your own products such as toiletries, cosmetics, perfumes or hair care products which you have talked about with your doctor as they, or you, think that you may be allergic to them. Please bring all the packaging that they came in with you as this may have the list of ingredients.

On your second appointment please bring: 

• Your smart phone if you have one. This is so it can be used to take photos of the area of your body where we put the patch tests.

How many patch test appointments will I have and when will they be?

You will have three appointments. These will all be at Southlands hospital.

• The first will be on a Wednesday morning 
• The second will be on the Friday morning (the same week as your first Wednesday morning appointment) 
• The third will be on the following Wednesday morning (one week after your first appointment).

Will having a patch test hurt?

No. Having a patch test should not cause you any pain. It does not involve you having any injections. The patch tests may feel a little strange on your skin.

What does patch testing involve?

• On your second appointment visit (we call this ‘day two’):

Please allow 20 minutes for your appointment.

1. We will remove the patch test strips and note what skin reactions you have had to them
2. We will show you how to take pictures of your patch tests using your smartphone (if you have one). 

Be aware any tape or pen marks that we have put on your back to show where the patches were must stay on your back until your third visit. This is so we can check if you have any further skin reactions after we have taken the chambers off. We will supply you with a skin marker pen for you to re apply if you feel they are fading. 

It is usual for your skin to feel itchy where you have had the patch test strips. 

If we cannot tell whether you have had an allergic (positive) reaction to one of the substances you have already been tested for we may re-apply it at this appointment. You will need to remove this strip at home on the next Sunday. We will explain this to you if you need to do it.

• The Sunday after your second appointment visit (when you are at home)

1. Please take pictures of the areas where the patch tests were if you can. We will have shown you how to do this on your second appointment visit.  
2. Please reapply the marker pen to the already marked out areas, if you feel they are fading.

• On your third visit (Day 7)

Please allow 30 minutes for your appointment.

1. We will check your back to see if you have had an allergic reaction to any of the substances in the patch test strips. A specialist nurse or doctor will talk with you about any allergic reactions you have had.

It is usual for your skin to still feel itchy where you have had the patch test strips. 

We should be able to tell If you have an allergy to any of the substances in the patch test strips by the third time we check. If your skin has become red and itchy at the test site this tells us that you have had a positive reaction (you are allergic to a substance).

What happens if all the patches are negative?

If all the patches are negative (they show that you have not had an allergic reaction to any of the substances in the patches) this is still useful. It means that, as far as we can, we have ruled-out that a contact allergy is a cause of your skin problem. We can then look for other causes.

Are there any things which mean I may not be able to have a patch test?

Yes. There are some things which mean that it may not be safe for you to have a patch test or that the patch test may not work properly. 

Do contact us one week before your first patch test appointment if:

• you are pregnant or breastfeeding 
• you have a large area of eczema on your back or all over your body. 
• the area of skin where you would have the patch test (usually your upper back) has been in the sun (or you have used a sunbed) in the last six weeks. 
• you are on a dose of steroid medicine which is over 10mg of steroid per day 
• you are taking a medicine that means your immune system does not work as well as usual. If you are unsure, please contact us for advice. We usually have to delay patch testing: 
  • for three months after you have finished taking any medicine that might cause your skins immune response to be less intense than usual (a medicine which suppresses your immune system) 
  • for six months if you are taking biologic medicines. Biologic medicines come from a living source (a human or animal) or its products. They act on specific parts of the immune system.

How should I care for my patch test strips so that they work as well as possible?

From the day of your first appointment until after your last appointment:

What else should I do, and not do, while I have the patch tests on?

Should I avoid playing sport, doing heavy physical activity and sexual activity while I have my patch tests on?

Yes. Try to avoid these.

What should I do if I have itching or unbearable irritation while I am wearing the patch tests?

If you have itching, take an antihistamine tablet. You can buy these from a supermarket or pharmacy. Follow the instructions on the packet.

It is very rare to get an unbearably uncomfortable reaction to one of the substances in the patch test strips. If you have this do remove the patches and tape and contact us.

What side effects could I get from the patch test?

Side effects are rare but can include:

• skin reddening (this may look different on black or brown skin), burning, itching and blistering from having an allergic reaction to one of the substances in the strips (a positive reaction). This usually disappears after a few days although it can last longer. 
• stains on your skin caused by the substances in the chambers. This usually disappears after a few days. 
• your skin may get lighter or darker where you have the patches. This is because you may get less or more pigment in your skin.  
• a flare-up of eczema. 
• infection or scarring where you have the patches. 
• an allergic reaction to the tape. 
• an ‘angry back’ reaction. This means that your skin reacts as if you are allergic to many of the substances. It may become itchy and red even though you are not really allergic to the substances. When it looks as though you are allergic, but you are not this is called a ‘false positive’ reaction.

Where can I find further information about patch testing?

You can find out more about patch testing on these websites:

• British Association of Dematologists leaflets: www.bad.org.uk/public/leaflets 
• Dermnet: www.dermnetnz.org/procedures/patchtests 
• British Society for Cutaneous Allergy: www.cutaneousallergy.org

Who should I contact if I have any further questions or concerns after I have read this information or if I have a skin reaction after my third patch test appointment?

Which allergens can the patch test help to identify?

The patch test is used to test for allergies to the substances in the following list. 

We will give you further information about any of the allergens to which you test positive. 

You can find further information about allergens and what they products they are found in on The British Society of Cutaneous Allergy web site.

1. Potassium dichromate 
2. Neomycin 
3. Thiuram mix  
4. Paraphenylenediamine (PPD) 
5. Cobalt 
6. Caine mix  
7. Formaldehyde 
8. Colophonium 
9. Quinoline Mix 
10. Peru Balsam 
11. N-Isopropyl-N-Phenyl-paraphenylenediamine (IPPD) 
12. Lanolin 
13. Mercapto mix 
14. Epoxy resins 
15. Parabens 
16. 4-Tert- Butylphenolformaldehyde resin (PTBP) 
17. Fragrance Mix I 
18. Quaternium 
19. Nickel  
20. Methylchloroisothiazolinone 
21. 2-Mercaptobenzothiazole (MBT 
22. Amerchol L-101  
23. Sesquiterpene lactone  
24. p-Chloro-m-cresol   
25. 2- Bromo-2-Nitropropane-1,3-Diol   
26. Cetearyl alcohol 
27. Fusidic acid sodium salt  
28. Tixocortol – 21  
29. Budesonide  
30. Imidazolidinyl Urea  
31. Diazolidinyl Urea   
32. Methyldibromo glutaronitrile  
33. Treemoss absolute  
34. Chloroxylenol (PCMX0) 
35. Carba  
36. Fragrance mix II 
37. Disperse blue   
38. Hydroxyisohexyl 3-cyclohexene carboxaldehyde 
39. Compositae  
40. Methylisothiazolinone   
41. Sodium metabisulfite   
42. Hydroperoxides of linalool 1% 
43.  Hydroperoxides of linalool 0.5%  
44. Hydroperoxides of limonene 0.3%  
45. Hydroperoxides of limonene 0.2%  
46. 2-Hydroxyethyl methacrylate  
47. Benzisothiazolinone 0.1%  
48. 2-n-Octyl-4-isothiazolin-3 
49. Decyl Glucoside 5%  
50. Lauryl Polyglucose