Here’s What Happens To Your Hair When You Dye It

23 May 2022 | Tincture and Colour

Ever had a moment where you wonder how the heck something actually works? Well, we can’t tell you why the sky is blue or how the world came to be, but we can, with full authority, explain how we’re able to colour our hair.

So, here’s exactly what happens to your hair when you dye it.


What chemicals are in hair dye?

Before we dive into what happens to your hair when you dye it, it’s important to understand the chemicals that are involved in dying your hair. After all, hair dying is a chemical reaction at core.

Person mixing hair dye chemicals together
  • Ammonia

Ammonia is the hair dye ingredient that you are likely most familiar with. If you’ve ever used box dye, you’ll remember that distinct sharp, suffocating odour that made your eyes water; that was ammonia.

Whilst it has a bad reputation, ammonia is a vital ingredient in hair dye. Without it, the hair dye would not be able to penetrate the hair shaft.

The reason it gets a lot of stick is because of drugstore box dye. Professional colour used in the salon also contains ammonia, but it only uses the amount necessary to lift the hair’s proteins.

Box dye, on the other hand, uses an excessive amount of ammonia which will inevitably cause damage no matter how healthy your hair is. Plus, you’ll have to deal with that rancid smell!


  • Hydrogen peroxide

Another ingredient found in most hair dyes is hydrogen peroxide. It is used as the oxidising agent or developer.

Essentially, hydrogen peroxide removes the pre-existing colour in your hair, whether that be your natural pigment or dye. This allows the new colour to bond to the hair cortex.


  • Paraphenylenediamine (PPD)

Have a go at saying this next ingredient aloud!

Typically, PPD is the primary colouring agent in your dye. It ensures that your colour is permanent, meaning that you can wash your hair without losing your colour.

Generally, the darker the hair colour, the higher the concentration of PPD.

As mentioned, hydrogen peroxide can be used as the oxidising agent in hair dye. As it so happens, PPD requires oxygen to become a dye, which is why permanent hair dye never comes in one bottle.


  • Ethanolamine

Ever wondered what is used in ammonia-free hair dye? Ethanolamine is your answer.

You might be thinking that ethanolamine is less damaging on your hair as it is used in ammonia-free dyes…

But let’s break the misconception; the only way to get a permanent hair colour is to use a dye containing corrosive materials. The hair cuticle needs to open to allow the colour to bond to the hair.

With that said, ethanolamine works exactly the same way as ammonia. The only reason you might choose an ammonia-free dye is if you experience asthma, or ammonia causes you scalp irritation.


This is what happens to your hair when you dye it

So, what happens to your hair when you dye it?

When hair dye is applied to your hair, a chemical reaction occurs which changes the structure of the hair shaft. Protecting the hair shaft is the hair cuticle, which is made up of keratin cells. Ammonia causes the cuticle to swell, revealing the cortex underneath.

The cortex is where you will find more keratin and, importantly, pigment proteins called melanin. This is what gives your hair its natural colour. As the mixture seeps into the cortex, hydrogen peroxide removes the pre-existing pigment and oxidises the dye.

In simpler terms, the existing pigment in your hair is replaced with your chosen hair colour.

Once the ammonia has evaporated, the cuticle shrinks to its original form, locking the dye molecules into your hair and leaving you with a permanent colour!



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What happens when you dye your hair too much?

Any kind of colouring will, inevitably, inflict some damage on your hair. Damage experienced at the salon will be minimal compared to using box dye, but nonetheless, when you change the structure of your hair strands, slight damage is unavoidable.

Depending on the execution, if you dye your hair once, you probably won’t notice any difference in your hair’s condition. If you use box-dye, you may notice that your hair feels finer and dryer.


But what happens when you dye your hair too much?


The chemicals in the hair dye are going to cause irreversible damage to your hair. Ammonia opens the hair cuticle (the protective layer), but if this is repeated enough times, it will weaken the structure of your hair. Peroxide will cause the hair to become straw-like and dry.

You may also notice that your colour doesn’t last as long when you constantly dye your hair. This is due to the cuticle being damaged, meaning the pigment molecules are not sealed.

When this protective layer is compromised, your hair will also be more prone to damage from everyday factors such as heat and UV rays. 

So, don’t box dye your hair too much. In fact, don’t box dye your hair at all. As expert hairdressers, we can ensure that your hair remains in its best condition at all times.


What happens if you dye your hair without bleaching?

We know that in order to dye your hair, the hair cuticle needs to open to deposit the colour molecules. So, what happens if you dye your hair without bleaching it first?

The answer is: it depends. If you have light brown hair and want to dye your hair black, then you do not need to bleach your hair first. This is because light brown hair has much less pigment than the black dye molecules, so the colour will take to your hair.

However, the opposite is not true. If you have dark hair and want to go lighter, you will always need to lighten your hair beforehand. This is because the darker your hair is, the more pigment it has, whereas the lighter your hair is, the less pigment it has.

So, to get a lighter hair colour, you need to remove the pre-existing pigment in your hair, which is what bleach does.



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Learn more about what bleach does to your hair in our recent blog, Why Does Bleached Hair Turn Yellow?


Does semi-permanent hair dye penetrate the cuticle?

Semi-permanent, demi-permanent and gloss hair colours usually do not contain ammonia, and therefore do not penetrate the hair cuticle.

Instead, the colour molecules are deposited on top of the cuticle. Depending on how porous your hair is along with your colour maintenance, your hair colour will last around 10-12 washes.


Get your dream hair colour at Tierney Salons UK

Whether you want a fresh new colour or need some colour maintenance, you should consider visiting the best hairdressers in Hertford (psst…that’s us). 

Our team of expert hairdressers will look after your locks with utmost care and skill. In fact, the latest addition to Tierney Salons, Beth, is an expert when it comes to creating incredible colours.

Book your first appointment with Beth here.