• Reference Number: HEY1299/2025
• Departments: Dermatology
• Last Updated: 31 August 2025

Introduction

This leaflet has been produced to give you general information about your procedure. Most of your questions should be answered by this leaflet. It is not intended to replace the discussion between you and your doctor, but may act as a starting point for discussion. If after reading it you have any concerns or require further explanation, please discuss this with a member of the healthcare team caring for you.

What is a Patch Test?

You have probably been troubled by some symptoms and following discussion with your doctor a patch test has been arranged. Patch tests establish if you have any allergies to things you come into contact with in the environment, for example in creams, washing products, dyes and many more items.

You will be tested with a number of substances most common in contact allergy. These include: perfumes, metals, preservatives and rubber. The doctor, depending on your skin problems, may have arranged extra patch tests

The different substances are placed in hypoallergenic adhesive patches which are applied to your back. The substances remain in place for five days and you can then be assessed for allergic reactions

Why do I need Patch testing?

Patch testing is a way to find out if you are allergic to anything that is coming into contact with your skin. The symptoms you have been having mean this may possibly be the cause. If the tests are positive, then you will know what substances to avoid in the future. However, we cannot patch test all substances, so you will still need to monitor your skin and do your own research. Also, allergies can change over time. Some people prefer to avoid certain substances; if they know they cause a problem and do not feel testing is required. However, for some people the tests identify a substance, which they were not aware of and can monitor in the future.

Can there be any complications or risks?

Patch testing is not advisable if you:

• Have a widespread rash on your back
• Are pregnant or breastfeeding
• Have had sun exposure or used a sun bed in recent weeks
• Are taking immunosuppressant’s medication. Some may be acceptable, however, please discuss this with your doctor or nurse
• Are taking oral steroids. Some doses may be acceptable, please discuss this with us before stopping any medication

If any of these apply, please contact one of the nursing staff

Side effects are uncommon, but may include:

• Ongoing reaction – a very small number of reactions may persist for up to a month
• Sometimes substances may temporarily stain the skin
• Skin colour change – colour may o=increase or decrease at the site
• Allergy – very rarely, you may become sensitive/allergic to one of the test products
• Flare up of a skin condition – positive reactions can trigger a flare
• Infection or scarring – these are rare
• Rarely, severe reactions can produce small ulcers on the skin, which require topical treatment.

How do I prepare for the Patch Test?

Please read the information leaflet. Share the information it contains with your partner and family (if you wish) so that they can be of help and support. There may be information they need to know, especially if they are taking care of you following this examination.

Creams and ointments applied to your back should be avoided for 24 hours prior to patch testing.

It is advisable to trim any excess hair on the upper back area 24 hours before having your patch tests applied as this helps them remain more secure. Ideally, you should not shave your back.

What will happen?

Three visits to the hospital are required

First visit, Monday – Allow up to 30 minutes for this visit when small quantities of the test substances will be applied to your back. They are held in special chambers, covered by hypoallergenic tape and will be left in place for 48 hours. Please contact us if you have previously reacted to medical adhesive tapes or plasters. The locations of the chambers are marked on your skin with washable ink. Sometimes the arms or thighs are also used

Second visit, Wednesday – the chambers are removed and any reactions recorded. The nurse will re-mark the sites with ink. Please continue to keep the areas dry and apply no creams or ointments until after your third visit 48 hours later

Third visit, Friday – your back will be examined for any reactions. Red and itchy skin will occur with positive reactions, which will usually be visible for reading by the nurse on the Friday visit. Occasionally late reactions may appear, up to 10 days after application. Please contact the department in this case. Most reactions will disappear after a few days.

What happens afterwards?

The nurse will discuss any positive reactions with you and relevant information will be provided.

Should you require further advice on the issues contained in this leaflet, please do not hesitate to contact the Dermatology Department on tel: 01482 622262.