Allergy patch test

Patch Test for Allergic Contact Dermatitis?

Allergic contact dermatitis is an inflammatory reaction that occurs when substances to which you are allergic come into contact with your skin. The reaction, which is is a kind of eczema, makes the skin red, cracked and itchy or sore. The condition may required repeated exposure to the substance over a period of time to develop. Substances that commonly cause contact dermatitis can be found in your perfume or aftershave, hair dyes, various ointments and skin creams, household cleaners, metal jewellery and even in the materials in leather shoes and rubber boots. The oils, greases and coolants used in various industries may also cause the condition.

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What is a patch test?

The patch test is used to identify any substances that are causing your skin problem, so that you can avoid them in future. Preparing for the patch test You will be asked to stop using any steroid creams or taking steroid tablets for at least two weeks before you attend the clinic for the test.

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How the patch test is carried out

Your skin will be exposed to small amounts of different substances which might be causing your skin condition. These substances may be applied as ready-for-use 'panels' on special adhesive dressings, or the clinic will dispense the test substances into small chambers set on an adhesive plaster. The dressings will then be applied to your back so that the various substances are in contact with your skin. If you are allergic to any of the test substances it will cause redness of the skin where it is in contact. This reaction will usually develop within 48 hours and persist for a few days. Once the dressings have been applied you will be sent home with an instruction not to remove the dressings or get them wet for 48 hours. After 48 hours, ask someone to help you remove the dressings. Your doctor may ask you to take a photo.You will then return to the clinic after a further 48 hours. Try to keep the test area clean and dry until your final visit. Reading the results At the final visit to the clinic, your back will be examined for any reactions that have persisted after the dressings have been removed. The doctor will discuss the results with you and give advice on allergen avoidance or prescribe other treatment. You will also be asked to report any further reactions that appear within the next few days. Most reactions will appear during the 96-hour test period, but some reactions can take as long as 10 days to appear. The clinic will be able to tell you how long it will be likely to take to complete your testing based on your history and symptoms.

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Frequently asked questions

What if my skin gets itchy or burns under the dressing? An itching sensation is quite common. Try not to scratch the patch test area as this can make the itching worse and affect the interpretation of the results. If the itching/burning becomes severe please contact the clinic.

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What if my patch test starts to come off?

You can use a hypoallergenic adhesive tape to reattach the dressing. Apply the tape around the edge of the dressing only. Will I really not be able to shower? You should minimise contact with water. If your clinic has used a water-resistant covering you will be told whether or not you can shower. Even after the patches are removed, you should try to limit showering and avoid scrubbing the test area until after the doctor has examined the reactions.

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Can I go to the gym?

Depending on the type of dressing used, you should be able to have a light workout, but it is recommended to check with the clinic beforehand.

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What if my results are negative?

Negative results are common. Patch testing helps to narrow the range of potential allergens causing your reaction. If all your initial tests are negative, the clinic will reassess your history and test you again with a different set of allergens. The process of elimination will continue until the specific cause of your allergy is identified.

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