What is Patch Testing?

What is Patch Testing?

Patch testing is a procedure used by our hair stylists and colour technicians before applying hair colour to the scalp. It is a simple and safe way of identifying whether the hair dye that the stylist intends to use will cause an allergic reaction with the skin.

The reason patch testing is used is to ensure that the chemicals in the hair dye are safe to use on the client.

Why is it Necessary?

Patch testing is essential to ensure that the active ingredient, Paraphenylenediamine, does not cause an allergic reaction.

Paraphenylenediamine is an active ingredient that is often used in hair dyes as it produces a very natural look.

Hair salons will use a patch test to ensure the safety of their clients by using a small amount to see if the Paraphenylenediamine in the hair dye causes a reaction on the skin.

A patch test is only required when hair dye comes into contact with the scalp. However it is still importatnt to do a patch test for other colour treatments such as hair highlights where foils are used, as the foils can leak and come into contact with the skin.

What Does it Involve?

The patch test will usually be done 48 hours prior to the appointment. If the test produces a reaction the client’s skin then the hair dye, then the hair dye should not be applied.

Prior to the patch test the stylist will ask you a few questions to ensure that it is safe for us to apply the colour sample to your skin for the patch test.

The stylist will then apply a small amount the hair dye mixture on the skin, usually behind the ear and advise the client that it should not be washed for the next 48 hours.

What are the Risks?

A reaction from Paraphenylenediamine usually just results in dermatitis to the eyelids or ears. It may also result in swelling to the face.

A severe allergic reaction to Paraphenylenediamine could result in contact urticaria and in extreme cases, anaphylaxis.

People working with Paraphenylenediamine can develop a sensitivity resulting in Dermatitis in the hand.

What Should I Do if I Have a Reaction?

If you do have an allergic reaction to the patch test you will not be able to use any oxidation type hair dyes.

You should also alert your Doctor to let them know that you have had an allergic reaction to Paraphenylenediamine.


Patch testing is an essential procedure to ensure the safe use of hair dye. Whilst it may be a little inconvenient to visit your stylist 48 hours before your appointment it is essential to ensure your safety.

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