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Patch testing


What are the aims of this leaflet?

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 potential side effects are.

What is patch testing?

Patch testing is a specialist procedure carried out by dermatology doctors and dermatology nurses to find out whether your skin condition is caused or aggravated by an allergy to substances which have come into contact with your skin. This is called contact allergy.

Substances that cause an allergic reaction are called allergens. They can be found at home, at work or in leisure activities.

What will be tested?

There are approximately 40 substances which are most frequently in contact with the skin such as natural rubber latex, preservatives, metals, perfumes, cosmetics, leather chemicals, lanolin and plants among others. Additional substances are sometimes added to this list if it is thought they may trigger your skin condition. You may also be tested with 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 those prescribed and those you may have bought yourself.

  • Your own products- items you use at home which you think may be causing or worsening your skin condition such as toiletries, cosmetics, nail polish, perfumes and hair products. If you put any products directly on your skin then please bring both the product and the packaging, including the leaflet, where the ingredients are listed. For other items such as household cleansers, washing powder and fabric softeners, it is only necessary to bring the packaging showing the list of ingredients. If you have been asked to bring any particular product or substance, it is important to remember to bring them with you.

  • Products and chemicals used at work -if you think that substances at work may be making your skin condition worse please bring in the Health and Safety Data sheets (sometimes called the COSHH sheets) of these products. These will be available at your place of work although you may need to speak to the Head of Health and Safety. You may be asked to bring samples of these products for testing, if necessary.

What does patch testing involve?

Three visits to hospital are required.

On the first visit, each substance to be tested will be applied to your back in special small disc (about 1cm in diameter) containers held in place by hypoallergenic tape. The location of the containers is identified by marking your back with ink. Occasionally the arms or the thighs are also used to patch test. Itching of the test areas is normal, but you are strongly advised not to scratch. You should allow up to 2 hours for this first visit.

The substances will remain taped in place until your next visit, when the taping is removed and any reactions noted. Additional patches are sometimes added at this stage. The marking ink and/or tape will remain on your back for a further two days.

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

It may be necessary to expose part of your arm or back to ultraviolet light if a reaction to sunlight is suspected. This is called ‘photopatch testing’.

It is possible that your patch tests will be negative, but this is helpful to your doctor as contact allergy will be ruled out as a cause of your skin problem. Positive reactions become red and itchy where the substance was put on your skin, and usually become obvious by the third visit (final reading), although a reaction can occasionally take up to two weeks. If you do develop a late reaction, please contact your clinic. Some substances may stain the skin; this is normal and will wash off after a couple of days with showering or bathing.

Your doctor may decide not to patch test if you are pregnant, breastfeeding, have extensive eczema on your back, have a suntan or have applied an artificial suntan, have used a sunbed in the previous 2 weeks, are on a moderate or high dose of steroid tablets or are taking immunosuppressive drugs. If in doubt or if any of these apply, please telephone the clinic to rearrange your appointment.

Do not:

  • Do not get your back wet or bath, swim or shower during the week of the tests. A cool shallow bath is a good alternative.

  • Do not wear cherished or pale-coloured clothing as the tests and the marker ink may permanently stain it.

  • Do not expose your back to the sun or artificial sunlight (sun lamps) during testing.


  • Do avoid sport or heavy physical work during the week of the tests, as sweating will 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 to protect the patches. 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, tape the edges down using Micropore or ScanPor. If a whole patch comes loose, remove it and note the time and date.

  • Contact your clinic if you are concerned.

What side effects may occur?

Side effects are rare, but include:

  • Skin reddening 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.

  • Persistent reaction -some positive test reactions may remain for up to a month before fading away.

  • 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 pigment may be seen at the place where the patches are, which may last for months or rarely (1 in 1,000) be permanent.

  • Infection -this is rare and would need antibiotic treatment.

  • Scarring -very rare (1 in 10,000).

  • Allergy -rarely (1 in 5,000 patch tests), you may become allergic to one of the substances applied during patch testing. In practice, this does not appear 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 medical centres.

Where can I get more information about patch testing?

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

For details of source materials used please contact the Clinical Standards Unit (

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: individual patient circumstances may differ, which might alter both the advice and course of therapy given to you by your doctor.

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






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