How to do a patch test for hair dye | The ultimate guide.

You’re ready for a new do, a new you and a fabulous new colour. You might be taking the plunge with bleach, or maybe you’re topping up your roots with a hair dye you’ve never used before. All of these are reasons why you’ll need to how to do a patch test for hair dye.

We’re here with everything you need to know about patch tests, how to do them and why it’s so important not to skip, even if you’ve been using hair dye for years. Read on!

How to do a patch test for hair dye

What is a patch test?

This is a very important test you carry out to check that you’re not going to have any nasty allergic reactions to a product. It’s typically carried out 48 hours before you want to dye your hair. This gives it enough time for your skin to react if it’s going to.

Certain chemicals and ingredients in hair dye can cause adverse allergic reactions and doing this check is a safe way of making sure your hair dye is not going to swell up your head and put you in hospital. (Soz to be dramatic!).

Patch tests are not just for hair dye products either. It’s wise to test for allergens if you have sensitive skin and are trying new cosmetics, moisturisers, soap, or topical creams.

It’s often confused with a hair dye strand test. But a strand test is nothing to do with allergies. It’s a test that involves putting hair dye on a few strands of hair to check that the hair dye colour result is the one you really want.

Why do I need to do a patch test?

Plenty of people skip this part of hair dyeing to save time or because they think the hair dye won’t affect them.

But when it comes to home hair dyeing, even if you’re used to certain brands, others may cause a reaction.

And in fact, the more you are exposed to chemicals in hair and even products like fake tan, the MORE chance you have of having a reaction.

So it’s best to do this quick and simple test, be safe and check rather than rush into something that could have nasty results.

Tools for keratin treatment. brush, bowl and hair dye in tubes top view

Where on the body do you do a patch test?

We recommend starting with a small section at the nape of your neck or behind one ear.

You can also try applying the hair dye onto skin where there is little-to-no hair growth (such as your forearm) followed by an inconspicuous spot like inside your elbow crease.

It actually doesn’t matter WHERE you apply the dye as you’re testing your body’s reaction to it, not just your hair and head.

The most common areas of sensitivity on the body are the neck, chest, back of arms, hands and lower legs. So any of these spots will do!

How long does a patch test take?

There are few things more important in the world of beauty than ensuring your skin isn’t irritated or broken by the products you use.

You’ll need to do the test at least 24-48 hours before. This is to give the dye enough time to be on your skin and know if it’s going to cause any adverse reactions.

Try it in the morning so you have a whole day to watch for reactions.

Though this may seem time-consuming and unnecessary, having a little patience will help ensure that you get your perfect hair colour without any drama.

How to do a patch test for hair dye step-by-step.

Follow these easy steps to do your test easily at home!

Step one: Mix your hair dye.

To test the dye, you’ll have to open it and mix a small amount of the developer and the colourant as if you were going to dye your hair.

It only needs to be a pea-sized amount of each substance. Don’t mix the whole activator and dye together as it won’t last for 48 hours until you dye your hair.

TOP TIP! Hair dye is often on offer. You can buy two boxes of hair dye and use one for the test!

Step two: Apply the dye.

Using a cotton bud or Q-tip, dab a small amount of dye on a clean area of skin.

Because the hair dye is going to go on your head, the best place to put it is behind your ear on your neck. If you do have a reaction, it won’t be too obvious or unsightly.

However, some people prefer to place it on their inner arm.

Step three: Wait and watch.

Once the dye is dry, leave it on for 48 hours to do its thing.

If it starts to itch, burn or a rash, swelling or redness begins to develop, it’s safe to say your skin is not happy with this hair dye and you can wash it off.

Allergic reactions can be very serious. If your symptoms are worsening, you may need to call emergency services for help. You find out more about the types of allergic reactions you can have to hair dye on the NHS website here.

Step 4: No reaction? No problem.

If 48 hours later, your results are clear and everything looks as it should, you can do a little skip for joy and crack on with your hair dyeing process! Good luck!

Watch and learn: How to perform a patch test

What happens if I am allergic to hair dye?

The ingredient in hair dyes most often responsible for a reaction is para-phenylenediamine (PPD), which is used in many permanent hair dyes.

There are safe and ‘natural’ hair dyes you can try, but you will need to read the ingredients on the box very carefully to make sure they are truly PPD free.

PPD is the most common allergen, but you should visit your doctor if you have had a reaction so they can pin point the cause and make recommendations that are right for you.

No one should be deprived of colouring their hair! So play it safe and make sure you do a hair dye test!

Guide to the perfect patch test


  • Do conduct the test 48 hours before you are due to dye your hair. Any time is fine but we prefer the morning so we have all day to watch and wash it off if we need to.
  • Do mix up only a small amount of hair dye for test, not the whole bottle (unless you have bought an extra box especially for the test).
  • Do apply it to the back of your ear on your neck. It is ok to apply it elsewhere to test the contact of it on your skin. But since this is hair dye, we’d opt for your head.
  • Do wash it off immediately if you are experiencing any adverse reactions.


  • Don’t skip it! Even if you are a hair dyeing pro, you can still react badly to the chemicals. In fact, the more you have been exposed to hair dye, the more likely you are to have a reaction.
  • Don’t leave it on if you start to feel any itching, burning or swelling or if you notice a rash developing. Wash it off immediately. That hair dye is not for you!
  • Don’t just try another hair dye brand if you do have a reaction. The chances are it will contain the same ingredients you are reacting to. See your doctor to get to the root (sorry!) of the problem.

Parting words

In this blog post, we’ve covered the basics of how to do a patch test for hair dye.

We hope you found our tips helpful!

It’s important that you take precautions when using any product that could potentially have an allergic reaction on your skin or scalp.

Remember, if in doubt ask a professional. Good luck!