Why Does Bleached Hair Turn Yellow? Let’s Talk Science

23 March 2022 | Tincture and Colour

Every blonde dreads the day they go to brush their hair in the mirror, only to find strands of sickly yellow going through their locks.

But why does bleached hair turn yellow? Why are blondes destined to this tragic problem?

Get your white coats and goggles out, because we’ve broken down why exactly bleached hair turns yellow with some simple science, along with tips as to how to keep blonde hair from turning yellow.


What happens to your hair when we bleach it?

Before we look at why bleached hair turns yellow, we need to understand what is actually happening to the hair when we bleach it. So, let’s talk science and get on the same wavelength when it comes to bleaching.

We’ll start by looking at our handy colour chart below.

Hair colour chart showing levels from light to dark


Let’s say that you are currently a level 3 and want to achieve a level 9. The difference between these two colours is that level 3 is darker, and level 9 is lighter, right?

Well, when a hair colour is darker, what this really means is that it has more pigment, which is called melanin. The same is true for skin colour. For those interested, there are actually two types of melanin in the hair:


  • Eumelanin: the more of this, the more brown, black or red the hair will be.
  • Pheomelanin: the more of this, the more orange to yellow the hair will be depending on depth.


The light curve below actually shows how the brown mid levels have red and orange undertones.

Light curve showing dark to bleached hair levels


But what about blonde hair shades? Lighter hair, like the level 9 you see in our colour chart, is actually just hair with little to no pigment. If you imagine stripping all of the pigment out of level 3 hair, level 9 is what would be left underneath.

Believe it or not, stripping the pigment from the hair is exactly what bleach does. 


The chemistry of hair bleach

We’re not done just yet. Channel your inner “woman in STEM” and let’s crack the code as to how bleach works.

When bleach is applied to the hair, it causes a chemical reaction between the bleach and the pigment. This causes the melanin molecules to turn colourless. We know what you’re thinking – if it’s colourless then why isn’t my hair clear?

Firstly, that would be pretty cool. But secondly, the hair appears yellow because of keratin, which is the structural protein in the hair.

If your hair turns brassy after bleaching, this might mean you naturally have more pheomelanin in your hair. Bleach doesn’t react as easily with red hair, so after lightening, you might see some hints of gold or red left behind.

But of course, any yellow or brassiness can be fixed with a widely celebrated and adored colour product…the one…the only…HAIR TONER! 


Why does bleached hair turn yellow?

So we face the big question: why does bleached hair turn yellow? 

  • Bleached hair turns yellow because hair colour will inevitably fade

To recap on the chemistry of bleach, you’ll remember that when the hair is lightened, the pigment is stripped to reveal natural underlying yellow hues. Most hair just simply doesn’t lift past this stage to a white colour.

So, if you go to the hair salon and get the most amazing hair foils with a toner on top, unfortunately, that toner will fade until the yellow is revealed underneath.

It is truly unfortunate, but the bottom line is that all colour eventually fades; although we have “permanent” hair dyes, these actually are only intended to last 6-8 weeks.


  • Your tap water could be causing yellow discolouration

This might come as a surprise, but your shower water could also make your hair turn yellow faster. Hear us out…

Lightened hair has very high porosity. This is because the bleaching process opens the hair cuticle. In turn, this means that the hair will absorb whatever it is exposed to.

Your hair will mainly be exposed to your tap water due to hair washing. This water is actually filled with metals and minerals, and since blonde hair is very porous, these will be absorbed, causing a slight yellow tint.

You may also have heard that blonde hair turns green in swimming pools. This is true, and is due to chlorine in the water. The simple way to prevent this is to wet your hair in normal water first, which will get absorbed rather than the chlorine. You learn something new every day!


How to keep blonde hair from turning yellow

Blonde hair with no yellow
  1. Try using a shower filter

If you are starting to see discoloration in your blonde hair, it could be worth trying a shower head filter. These filter the water at the head as opposed to having to add a whole filtration system to your shower.

These are not only great for coloured hair, but can be a blessing for your skin if you suffer with dryness or irritation. You’ll be silky smooth from head to toe!


  1. Wash your hair less frequently 

Whether you have access to filtered shower water or not, washing your hair less frequently is an absolute must. Every time you wash your hair, it will inevitably cause your colour to fade. It simply cannot be avoided.

But anyway, washing your less will also improve its health, since you won’t be stripping it of its essential natural oils. 


  1. Avoid clarifying shampoos

If you come across any clarifying shampoo, immediately position yourself at least 10 metres away from it. If you use clarifying shampoo on your freshly toned blonde hair, you’re asking for that hair toner to go straight down the drain.

In case you didn’t know, clarifying shampoo is a stronger shampoo which is designed to work through and remove product buildup on the hair and scalp.

Whilst we do not recommend you touch it after a new toner, it can be useful to use it before your next hair appointment to create a more even, clean base for your fresh colour.


  1. Use purple shampoo correctly

You might think that purple shampoo is going to save your hair from discoloration. Whilst it probably won’t turn yellow, it will in fact turn muddy and green when used incorrectly, which is definitely worse.

Just like clarifying shampoo, it isn’t advised that you use purple shampoo after a fresh toner. Purple shampoo can actually strip the hair of the toner, which will likely leave you with a mixture of yellow, ashy and grey tones throughout your hair.

Learn more about using purple shampoo correctly in our previous blog, How To Maintain Blonde Hair here


  1. Visit the salon regularly 

We’ll say it once more: bleached hair will eventually turn yellow. However, that doesn’t mean you have to let your hair turn yellow.

With regular hair salon visits, you’ll never see a strand of yellow in your hair. We recommend visiting every 6-8 weeks for optimal maintenance results.


Summary: How to keep blonde hair from turning yellow

  1. Try using a shower filter
  2. Wash your hair less frequently
  3. Avoid clarifying shampoos
  4. Use purple shampoo correctly
  5. Visit the salon regularly


Get your dream blonde at Tierney Salons Hertford

Whether you’re looking to go blonde or simply want to maintain your current colour, you should consider visiting the best blonde 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 beautiful blondes.

Book with Beth here.