Hairdressing isn’t just an art — it’s applied chemistry. Every time we lighten, darken, perm, relax, or even wash hair, we aren’t simply changing appearance — we are driving molecular reactions inside a complex biological material.
This blog explores what happens chemically within the hair fibre, how colouring and other chemical services work, and even how natural environmental forces trigger chemical change.
01 — The Chemistry of Hair Itself
Hair is a fibrous protein composite made mostly from α-keratin, a structure rich in:
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
- Nitrogen (N)
- Sulphur (S) — the key player in chemical services
Structurally, hair has:
| Layer | Composition | Chemical relevance |
|---|---|---|
| Cuticle | Overlapping keratin scales | Controls porosity and barrier to chemicals |
| Cortex | Long keratin chains and pigment granules (melanin) | Where colour reactions occur |
| Medulla | Central canal | Minimal chemical role |
Major chemical bonds in hair
| Bond | Strength | Role | Broken by |
|---|---|---|---|
| Disulfide (S-S) | Very strong | Shape and strength | Perms / relaxers / strong oxidisers |
| Hydrogen | Weak | Temporary styling | Water and heat |
| Salt (ionic) | Moderate | Texture stability | pH changes |
Understanding bond behaviour is essential: every salon chemical service modifies these bonds differently.
02 — Hair Colour Chemistry: Manipulating Melanin
Natural hair colour comes from melanin polymers — mainly:
| Eumelanin | Black / Brown | More resistant to degradation |
| Pheomelanin | Red / Yellow | Sulphur rich — produces warmth when lightened |
Permanent Colour — Oxidative Chemistry
Permanent dyes operate in three key reactions:
1️⃣ Cuticle swelling
Alkaline agents (usually ammonia) raise pH and open the cuticle.
2️⃣ Melanin oxidation
Hydrogen peroxide breaks down natural pigment.
3️⃣ Dye formation inside the cortex
Small molecules polymerise into large coloured molecules trapped in the hair.
This is why permanent colour does not wash out — the colour molecules are too large to escape.
03 — Bleaching: Oxidation on Overdrive
Bleach contains:
- Persulfates — radical generator
- Hydrogen peroxide — oxidises melanin
Melanin is progressively broken into lighter fragments.
Why bleach weakens hair
Oxidation can also weaken disulfide bonds, reducing structural strength.
04 — Toning: Colour Neutralisation Chemistry
The colour wheel helps professionals neutralise unwanted tones after lightening.
Understanding the colour wheel helps colourists select the correct toner to achieve balanced results.
05 — Perming & Relaxing: Reshaping Sulphur Bonds
Both services rely on breaking and reforming disulphide bonds.
Perming process
- Disulphide bonds reduced
- Hair reshaped around rods
- Bonds re-oxidised to hold new shape
06 — Natural Environmental Chemistry
| Factor | Chemical effect |
|---|---|
| UV radiation | Photo-oxidation of melanin |
| Swimming pools | Copper deposits create green tones |
| Hard water minerals | Metal build-up interferes with colour |
| Heat styling | Cuticle cracking and protein degradation |
07 — Why Consultation Matters
- Porous hair → unpredictable colour results
- Henna or metallic salts → dangerous chemical reactions
- pH history influences colour processing
Professional colourists aren’t simply choosing shades — they are managing chemical reactions safely.
How we control chemical reactions in the salon
An incompatibility test helps determine whether previous metallic dyes or treatments could react dangerously with colour or bleach.
Conclusion: Hairdressing = Chemistry in Action
Hairdressing is one of the clearest examples of real-world chemistry in action. From oxidation reactions in colouring to bond restructuring in perming, professional stylists apply chemical knowledge safely to create beautiful results.
Frequently Asked Questions
Is hair colouring really chemistry?
Yes. Hair colouring involves controlled chemical reactions that alter natural pigments and create new colour molecules inside the hair fibre.
Why does bleaching weaken hair?
Bleach oxidises melanin but can also damage disulphide bonds in keratin, reducing the structural strength of hair.
What is the role of hydrogen peroxide in hair colouring?
Hydrogen peroxide oxidises natural melanin pigments and activates dye molecules that develop colour inside the hair.
Why do professionals perform hair consultations?
Consultations help determine hair condition, previous chemical history and the safest way to achieve the desired colour result.
Contact Shape Hair & Beauty
📞 01273 474764
📧 shblewes@gmail.com
🖥️ https://shapelewes.co.uk/contact/
🏢 22 Valence Road, Lewes, BN7 1SH
