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Patient Information Leaflet

Patch Testing

What are the aims of this leaflet?

This leaflet has been written to help you understand more about patch testing.

What is patch testing?

Patch testing can help your doctor find out whether your skin condition is caused by an allergy to substances which come into contact with your skin, such as products at home, at work or in leisure activities. You can then be advised of the names of any identified allergens in order to help you to avoid them.

To what will I be tested?

You will be tested to around 40 standard substances which are frequently in contact with the skin, e.g. rubber, preservatives, metals, perfumes and plants, and also additional substances that are suspected triggers for your skin problem. You may be tested to some of your own work or home products, such as personal toiletries.

What should I bring to the patch test clinic?

On the first appointment please bring:

• A list of medication - any prescribed drugs you are taking.
  
• All ointments and creams - you use including over the counter creams.
  
• Your own products - items you use at home which you think you might be allergic to e.g. toiletries, cosmetics, nail polish, perfumes and hair care products (bring both the product and the packaging). For other items such as household cleansers, washing powder and fabric softeners, it is only necessary to bring the packaging, which should list the contents. If bringing plants, they should be put in paper bags or envelopes. If you have been particularly asked to bring any product or substance, it is important to remember this.
  
• Work chemicals - if you think that substances at work may be aggravating or causing your rash, please bring in samples in well-sealed labelled containers at least 2 weeks before your appointment. At the same time, please 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).

What does patch testing involve?

Three visits to hospital are required. On the first visit a dermatologist or specialist nurse will decide which tests are needed. The substances to be tested will be applied to your back in special small containers contained within a tape. The containers are identified by marking your back with ink. Occasionally the arms or the thighs are also used. Itching of the sites is normal. Allow up to 2 hours for this first visit.

The substances remain taped in place until your next visit, when the patches containing them are removed and any reactions noted. In some departments patients are asked to remove the patches an hour before the appointment.  Additional patches may be added, as indicated by the initial patch test readings. Marking ink or tape will remain on your back and may be reinforced, to ensure it will persist for a further two days

On the third visit, your back will be examined and any further reactions discussed with you.

It might be necessary to expose part of your arm or back to ultraviolet light if  a light-induced contact allergy is suspected (this is called ‘photopatch testing’).

It is possible that your patch tests will be negative. This is helpful since, as far as we can, we will have eliminated contact allergy as a cause of your skin problem. Positive reactions become red and itchy at the test site and usually become apparent by the third visit (final reading), although they can occasionally take longer, up to two weeks. If you do develop a late reaction, please contact the clinic. Some substances may stain the skin; this is normal and will wash off after a couple of days with showering or bathing.

You may not be patch tested if you are pregnant, breastfeeding, have extensive eczema on your back, have a suntan or have used a sun over the previous 2 weeks, or are on a moderate or high dose of steroids (e.g. prednisolone tablets more than 10 mg/day). If any of these apply, please telephone to rearrange your appointment.

Do not:

• Do not get your back wet during the tests (from bathing, swimming, and showering. A cool shallow bath works well.
  
• Do not wear cherished clothing as the marker ink may stain it permanently. 
  
• Do not expose your back to the sun or artificial sunlight (sun lamps) during this procedure.

Do:

• Do avoid sport or heavy physical work during the week of the tests, as sweating would cause the patches to fall off.
  
• Do wear an old bra or shirt for the week of the tests and wear a shirt or vest to sleep in order to protect the tests. Clothes that open at the front can be easier to take on and off than those which go over your head.
  
• If a patch starts to peel off, reinforce with tape such as Micropore or ScanPor. If a whole patch comes loose, remove it and note the time and date.
  
• Contact the clinic if you are concerned.

What side effects may occur?

Side effects are rare, but include:

• Skin reddening and itching at the application site - from positive test results. This usually disappears after a few days.
  
• Persistent reaction - some positive test reactions, e.g. to gold, may persist for up to a month.
  
• Flare of eczema - a positive patch test may be accompanied by a flare of existing or previous eczema.
  
• Pigment change - an increase or decrease in pigment may be seen at the site of patch tests, which may last for months or rarely be permanent.
  
• Infection - this is rare and would need antibiotic treatment.
  
• Scarring - very rare.
  
• Allergy - rarely, in about 0.02% of patch tests, you may become allergic to one of the substances applied during patch testing. In practice, this does not seem to cause problems in the long term.

Storage of patch test results

For audit purposes, patch test results are often recorded in an anonymised computer database and used to standardise the results of patch testing nationally, in accordance with good medical practice. The anonymised data may be used for research and shared with other centres. 

Where can I get more information about patch testing?

http://dermnetnz.org/procedures/patch-tests.html

This patient information leaflet was written in conjunction with the British Society for Cutaneous Allergy. 

The British Skin Foundation fund vital research into all skin diseases.  To find out how you can help, please visit the British Skin Foundation website here.

This leaflet aims to provide accurate information about the subject and is a consensus of the views held by representatives of the British Association of Dermatologists: its contents, however, may occasionally differ from the advice given to you by your doctor.

This leaflet has been assessed for readability by the British Association of Dermatologists' Patient Information Lay Review Panel 

BRITISH ASSOCIATION OF DERMATOLOGISTS
PATIENT INFORMATION LEAFLET
PRODUCED JUNE 2010