Patch testing

What is a patch test?

A patch test is a specialist dermatology test to determine whether you are allergic to substances or ingredients that have come into contact with your skin (a contact allergy), especially if they've been used for a prolonged period of time.

These could be substances in skin care products (such as perfume, preservatives, cosmetics, plant material), jewellery, rubber, chemicals, etc.

When the substances cause an allergy, usually in the form of an eczema eruption, they are called allergens. The 50 most common allergens are included in patch tests.

For more information about the test please visit the British Association of Dermatologists.

Who is a patch test suitable for?

A patch test isn't a suitable test if you're looking into a food allergy or allergy that causes hives and hay fever. Instead this would be done through a blood test or skin prick test.

The test also isn't suitable if:

• You're pregnant
• You've had a course of oral steroids
• You've had sun exposure on your back.

What happens during treatment?

• Day one: A nurse will apply the allergens in patches (usually five) on your back
• Day three: The patches will be taken off and the locations of the patches marked using a skin
• Day five: You'll see a doctor to determine whether you are allergic to the substances applied.

The patches should be kept dry from water and sweat for five days.You should avoid showering, working out, swimming and any other activities that will cause the patches to come loose during the test.

You can also bring your own products, such as creams and perfume, so that we can test them if it is safe to do so. We're happy to test two or three of these products. Only leave-on products (such as foundation) are suitable to be tested. Wash-off products such as washing powder and shampoo aren't suitable.

What do the results mean?

If the skin becomes red and itchy where a certain patch was, this means that test was positive and you're allergic to the substance or ingredient that was tested.

If there's no reaction on the skin, that means the test was negative and you aren't allergic to the substances or ingredients tested.

However, this doesn't exclude the possibility that the substances may have simply caused irritation (a reaction where the skin is irritated due to frequent application of a product).