PATCH TESTING & SKIN ALLERGIES

Patch testing is a procedure to investigate if a substance or chemical may be causing a skin allergy. Many patients are unaware that there may be a skin allergy causing their dermatitis.

Allergic contact dermatitis occurs when someone becomes allergic to substances that contact the skin. Skin allergy (contact dermatitis) is common in Australia, and common allergens include cosmetics, fragrance, nickel, and preservatives.

Patch testing is quite different to the prick testing which is used to investigate hay fever. Patch testing is the most reliable way to determine an allergic cause for a skin rash.

Contact dermatitis may be the cause of dermatitis around the eyes, or dermatitis which flares up very suddenly. Many cases of hand dermatitis can have an allergic cause. Some patients may have long standing eczema since childhood which is aggravated later in life by a contact allergy.

Patch testing is done by applying small amounts of “allergens” onto a series of “patches” on the back. At least 60 patches are usually tested at once. The patches are applied on a Monday, and the test is read after it is removed on Wednesday and Friday the same week.

After removing the patches, the dermatologist reads your test and identifies any red areas that have reacted.

If you have positive reactions, you will then be given written information on how to avoid these substances. Complete avoidance of the allergen can be curative for cases of isolated contact allergy.

If you think you would benefit from patch testing to investigate your dermatitis, you will need to see the dermatologist first to discuss what you may need to be tested for. If you think you need to be patch tested, simply ask your GP for a referral.

FURTHER QUESTIONS

What does contact dermatitis look like?

Contact dermatitis often looks very similar to atopic dermatitis (eczema). However if the rash occurs suddenly or flares with certain products, then a skin allergy should be considered.

Common locations for allergic contact dermatitis are the hands, face, and around the eyes.

Who should have patch testing?

Patch testing benefits patients with a presumed allergic contact dermatitis. Some occupations are particularly prone to skin allergies, e.g hairdressers, bakers, beauty therapists, dentists and health professionals.

Patch testing can be very useful to investigate sudden flares in dermatitis, or new onset dermatitis.

How long does patch testing take?

The patch procedure takes a week to perform correctly. Patches are applied on Monday mornings, and then removed on Wednesday for the first reading. A second reading of the results is done on Friday.

How is patch testing different from prick testing?

Patch testing will help to determine the cause of an allergic rash. It will usually identify substances which contact the skin and cause an itchy red rash that can last for days/months or even years!

Prick testing is a much faster procedure which looks for substances that cause hives, hayfever and food allergies. If you think that you need prick testing, then we recommend discussing with your GP if you need to see an immunologist. Prick testing can be performed “on the spot” with an immunologist and is usually tested on the arm at the time of your appointment.

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Who does patch testing?

Dermatologists have the training to conduct specialist patch testing. Only a few dermatology clinics in Melbourne do the testing due to the special equipment and nursing staff required.

Patch testing is available at Melbourne City Dermatology, public hospital dermatology clinics and the Skin and Cancer foundation.

What does patch testing cost?

Standard testing is $520, which includes the three appointments needed on the week of your testing, the patches and equipment used, and handouts detailing how to avoid any allergens you react to. Medicare will rebate approximately half this amount if you have a valid referral from your GP.

Patch testing costs will be quoted in full prior to booking the procedure, if extra allergens need to be ordered especially for you, these are charged at cost price.

How do I prepare for patch testing?

When you see your dermatologist for the initial consultation, the procedure will be explained in detail, along with costs and appointments needed. You will be given written information to help you prepare for the testing.

Patch testing can’t be done while you have rash on your back, or if you are taking certain medications.

On the day of the testing you should bring in products you apply to your skin at home, such as shampoo, shower gel, moisturizer and sunscreen as we will test you for these as well.

You should also plan your week around the patch testing as you can not get the patches wet, this means modifying the way you wash, and avoiding exercise that will cause excess sweating. We recommend washing your hair the morning before the patch testing, and using some dry shampoo if needed. You can also wash your hair over a sink to avoid wetting the patches.