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Does hair colouring cause hair thinning?

Does hair colouring cause hair thinning?

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In fashion and grooming, it has become common to change hair colour, such as hair dyeing, bleaching, and colouring. Also, many people who suffer from thinning hair think that if they colour their hair blonde or brown, one that is similar to their scalp tone, it will be less noticeable.

The purpose of colouring their hair varies from person to person.

However, you have probably heard that both hair colouring and bleaching, damages the hair and scalp causing thinning.

In fact, when a client with thinning hair comes to our salon, we often hear them say "I used to mess with my hair colour when I was younger with high bleach and colour, and that's why my hair has thinned” when they first enter.

In this article,

we will explain how hair colouring, such as hair dyes or bleach, affects the hair, and whether they cause hair thinning.

How does hair colouring work?

Before we unravel the relationship between thinning hair and hair colour, we will first explain how hair colorants work.

The pH value at which hair is most stable is in the range 4.5-5.5, which is called the isoelectric point. If the pH value is lower than this isoelectric point, the cuticle closes and the hair becomes hard and rough to the touch.

This closing of the cuticle is called astringency; conversely, when the hair cuticle becomes alkaline, it opens.

This is also a state of loss of strength because the salt bonds (ionic bonds) in the proteins are broken due to the high pH value. This makes the hair more flexible and allows grey hair dyes and perm products to penetrate more easily.

Thus, by changing the pH value of the hair, it is possible to colour or bleach the hair.

Types of hair colorants

Hair colorants come in a wide variety namely quasi-drug 'hair dyes' and cosmetic 'hair dyes', which will be explained below.

Oxidative hair dye

This is the oldest hair dye product, and is still used by many hair salons for grey hair dyeing and for hair colouring. In addition to penetrating the hair and colouring it with dye materials, it uses hydrogen peroxide to decompose melanin pigment to dye the hair.

About hair dyes (quasi-drugs)

Hair dyes include bleaching and decolourising agents, and grey hair dye, which is a permanent hair dye and is generally a liquid solution used in hair salons. Specifically, they include the following.

Acid hair colour

Acid hair colour is a hair dye available in mass retailers. They do not fade, do not cause rashes and do not damage the hair. Acidic hair colour has a pH of about 3, so it has little power to penetrate the hair, so it does not dye the central part of the hair inside.

Hair manicure

Once used to add shine to the hair, but nowadays the purpose of adding colour has been added to this. The ingredients used in the formulation are almost identical to those of acidic hair colour

Does hair colouring cause thinning hair?

Hair dyeing or bleaching does not directly cause thinning of hair due to the hair colouring.

However, there are two indirect effects on the hair and scalp.

Thinning of hair

Hydrogen peroxide in the hair colour has such a strong acidic effect that it breaks down melanin pigment, which also damages keratin, the main component of hair.

This accelerates the so-called thinning of hair, a brittle hair condition that leads to split ends, hair breakage, and poor hair growth.

In addition, the brighter the hair is coloured, the higher the concentration of hydrogen peroxide water and the longer the treatment time, which results in more damage to the hair.

And because hair cells repeatedly divide and keratinise in the keratinisation zone as if pushing up keratinised cells (cells die and become keratinised cells), they extend towards the skin surface.

As they also cannot repair or recover from damage on their own, so once damaged by colouring or bleaching, the hair cannot return to its original state by itself.

This may make you feel as if “you have thinning hair”, that “your hair is not manageable”, that "your hair does not have volume”, or that “your hair looks thinner”. However, this is only a change caused by thinner hair and does not mean that the hair has become thinner.

Therefore, it is important to avoid colouring and bleaching agents and switch to organic colours.

Hair loss due to dermatitis, etc.

Strong concentrations of hydrogen peroxide and ammonia in colorants and bleaching agents can cause skin disorders on the scalp and must be handled with care.

There are cases of primary irritant contact dermatitis, in which the skin becomes inflamed due to contact with irritants.

Another case may be allergic dermatitis, where the body's immune system recognises that the substance is harmful and becomes inflamed.

If you experience an itchy or sore scalp in a hair salon or similar, immediately notify the nearest staff member.

Primary irritant contact dermatitis will go away as soon as it is wiped and washed off, but allergic cases are different.

Because it is slow-acting, it does not react until some time after it has been on the scalp or skin, so treatment may be delayed. Also, as the scalp is a difficult place to see for yourself, always visit a dermatologist immediately if you notice anything unusual.

These scalp irritations may cause temporary hair loss or impaired hair growth, but once the dermatitis has settled, the hair condition will return to normal.


Hair colouring such as hair dyeing and bleaching do not directly cause hair thinning.

Even if there is a possibility, it is due to temporary dermatitis right after colouring, that will be within six months to a year at most. Therefore, rumours and opinions such as “I bleached or coloured my hair years ago and it caused my hair to thin” are basically false.

It is also safe to say that hair colouring has no direct effect on AGA (male pattern baldness), which is a symptom of most thinning hair in men.

However, there are cases where commercially available self-colouring colorants are too strong and causes significant damage to the scalp, resulting in unexpected skin problems and hair loss problems to the user, so it is basically recommended to visit a specialised beauty salon with “semi-permanent hair dye” or other colorants that causes less damage.

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