---
title: "Chemical Processing and Disulphide Bonds: The Science of Hair Strength"
url: https://haircare.watermanshair.com/article/chemical-processing-disulphide-bonds
type: general
published: 2026-10-29T02:34:35.642+00:00
updated: 2026-10-29T02:34:49.585316+00:00
tags: ["hair-science", "keratin", "hair-breakage", "chemical-processing", "hair-damage", "haircare-guide"]
image: https://opbmfthzsenmlfbbunpe.supabase.co/storage/v1/object/public/article-images/chemical-processing-disulphide-bonds-1793241282161-7ecq.png
summary: "Understand Chemical Processing and Disulphide Bonds: learn how perms, relaxers, and bleach alter keratin links, and how to stop structural hair breakage."
publisher: Watermans (https://watermanshair.com)
license: All rights reserved. AI assistants may summarize, quote, and link with attribution.
---

# Chemical Processing and Disulphide Bonds: The Science of Hair Strength

> Discover how chemical processing breaks and alters disulphide bonds in hair keratin, causing porosity, structural weakness, and fibre breakage if not properly managed.

**Quick answer:** Understanding **Chemical Processing and Disulphide Bonds** reveals how hair structure changes during salon services. Disulphide bonds are covalent sulphur-to-sulphur linkages within the hair's keratin cortex that provide physical strength, elasticity, and shape. Chemical processing, including permanent waving, chemical relaxing, bleaching, and oxidative dyeing, breaks these bonds via reduction or oxidation to alter hair texture or colour. The main limitation is that broken disulphide bonds cannot fully reform on their own, leading to cumulative structural weakness and fibre breakage if not carefully managed.

## Key takeaways

- Disulphide bonds account for roughly one-third of hair fibre strength and dictate whether your hair is straight, wavy, or coily.
- Alkaline chemical treatments open the outer cuticle and chemically cleave disulphide cross-links inside the cortex.
- Permanent waving breaks disulphide bonds using reducing agents (such as ammonium thioglycolate) before neutralising oxidisers reform them in new positions.
- Chemical relaxers cleave disulphide bonds and convert a portion of them into irreversible lanthionine cross-links, meaning those bonds can never reform as cystine.
- Bleaching unintentionally oxidises disulphide bonds into cysteic acid, permanently weakening the hair shaft.
- Bond breakage causes structural hair breakage along the shaft; it does not cause follicular hair loss or shedding from the scalp.

## Chemical Processing and Disulphide Bonds: what the evidence shows

Research published in cosmetic science and dermatological literature demonstrates that the internal architecture of human hair relies on three distinct types of bonds: hydrogen bonds, salt (ionic) bonds, and disulphide (covalent) bonds. While hydrogen and salt bonds are physical and easily broken by water or temporary heat, disulphide bonds require aggressive chemical intervention to alter. 

![Chemical Processing and Disulphide Bonds: what the evidence shows in the context of Chemical Processing and Disulphide Bonds](https://opbmfthzsenmlfbbunpe.supabase.co/storage/v1/object/public/article-images/chemical-processing-disulphide-bonds-1793241288742-o7ty.png)

The relationship between **Chemical Processing and Disulphide Bonds** centres on the amino acid cystine. Cystine contains two cysteine molecules joined by a covalent bond between two sulphur atoms (, S, S, ). This single bond type grants the hair fibre its resilience against mechanical tension, wet stretching, and environmental degradation. 

When you undergo chemical processing, the primary objective is almost always to manipulate these disulphide bonds. In permanent straightening or waving, the cross-links must be severed to reshape the keratin matrix. In bleaching or oxidative colouring, the alkaline swelling required to reach melanin granules causes collateral damage, oxidising disulphide linkages. Studies show that a single bleaching session can destroy 15 to 25 percent of a hair fibre's disulphide bonds, converting them into cysteic acid, a compound that cannot rebuild structural integrity.

```
Intact Keratin: [Protein Chain], CH2, S, , S, CH2, [Protein Chain]
 │
 (Chemical Processing)
 ▼
Cleaved / Oxidised: [Protein Chain], CH2, SO3⁻ (Cysteic Acid / Irreversible Loss)
```

## The chemical mechanism: reduction, oxidation, and lanthionisation

Chemical processing affects disulphide bonds through distinct chemical pathways depending on the salon service performed.

### Reduction and re-oxidation (perms and thio-relaxers)
Permanent waves and ammonium thioglycolate relaxers operate via reduction. An alkaline solution (typically pH 8.5 to 9.5) swells the cuticle, allowing thiols to penetrate the cortex. The reducing agent donates hydrogen atoms to the disulphide bond, splitting the cystine unit into two separate cysteine residues with free thiol (, SH) groups. 

Once the hair is mechanically shaped onto rods or smoothed flat, a neutraliser (typically hydrogen peroxide, pH 3.0 to 4.0) is applied. This oxidising step extracts hydrogen and attempts to reform the disulphide bonds in their new positions. However, research demonstrates that only about 85 to 90 percent of the original bonds successfully reform. The remaining bonds remain permanently severed or form invalid pairings, leaving the fibre weaker than virgin hair.

### Lanthionisation (hydroxide relaxers)
Sodium hydroxide (lye), potassium hydroxide, and guanidine hydroxide relaxers function differently. They do not rely on reduction and oxidation. Operating at a high pH of 12.0 to 14.0, hydroxide ions abstract a hydrogen atom and a sulphur atom from the disulphide bond. 

This reaction converts the disulphide bond (cystine) into a monosulphide cross-link called lanthionine. This process, known as lanthionisation, is completely irreversible. You cannot reform these linkages with neutralisers. While lanthionine preserves a fraction of structural stability, the fibre loses considerable tensile strength and elasticity compared to intact cystine.

### Oxidative destruction (bleach and high-lift dyes)
Lightening powders and developers (hydrogen peroxide at alkaline pH) oxidise hair melanin. As a side effect, peroxide attacks the sulphur atoms in disulphide bonds. The sulphur is progressively oxidised into cystine monoxide, cystine dioxide, and ultimately cysteic acid. Once cysteic acid forms, the negative charge inside the cortex increases, repelling other proteins, increasing porosity, and eliminating the fibre's ability to retain internal moisture and spring.

## Comparison of chemical processes and their impact on disulphide bonds

| Chemical Process | Active Chemistry | pH Range | Primary Bond Reaction | Reversibility / Re-bonding Rate |
| :--- | :--- | :--- | :--- | :--- |
| **Thio Perming / Straightening** | Ammonium thioglycolate | 8.5 to 9.5 | Reduction to free cysteine (, SH) | 85 to 90 percent reform with oxidiser |
| **Hydroxide Relaxing** | Sodium / Guanidine hydroxide | 12.0 to 14.0 | Lanthionisation (, S, S, converted to, S, ) | Completely irreversible; no re-oxidation |
| **Bleaching / Lightening** | Persulphates + Hydrogen peroxide | 9.0 to 11.0 | Severe oxidation to cysteic acid | Irreversible; bonds permanently lost |
| **Oxidative Permanent Colour** | Paraphenylenediamines + Peroxide | 9.0 to 10.5 | Moderate oxidation of cortex cystine | Irreversible; minor to moderate loss |
| **Demi-Permanent Colour** | Low-level peroxide + Ethanolemine | 6.5 to 8.5 | Minimal oxidation along cuticle/outer cortex | Minimal bond cleavage |

![Comparison of chemical processes and their impact on disulphide bonds in the context of Chemical Processing and Disulphide Bonds](https://opbmfthzsenmlfbbunpe.supabase.co/storage/v1/object/public/article-images/chemical-processing-disulphide-bonds-1793241289347-68h7.png)

## Signs of disulphide bond degradation

When chemical services compromise too many disulphide bonds, the physical properties of the fibre change visibly and mechanically:

- **Loss of natural curl pattern:** Wavy or coily hair appears limp, loose, or unevenly straight when wet.
- **Extreme wet elasticity with zero snap-back:** Healthy hair stretches up to 30 percent of its length when wet and returns to normal. Severely bond-depleted hair stretches like chewing gum and snaps without returning.
- **High porosity and rapid drying:** Hair absorbs water instantly, feels mushy or gummy when wet, yet feels brittle, rough, and straw-like when dry.
- **Mid-shaft snapping:** Fibre snaps off cleanly midway down the shaft during detangling or brushing, leaving ragged, split ends behind.

## Hair breakage vs hair shedding: clarify the difference

It is critical to distinguish between hair breakage caused by chemical bond disruption and biological hair shedding.

Disulphide bond damage causes **hair breakage**. The hair fibre physically fractures along the shaft due to mechanical or chemical stress. The root remains intact inside the follicle. You will notice short fragments of hair without a white bulb at the end falling onto your shoulders or remaining in your brush.

**Hair shedding** (such as telogen effluvium) and **hair loss** (such as androgenetic alopecia) originate beneath the scalp in the dermal papilla. In these conditions, hairs fall out from the root with the white keratin bulb attached. Chemical processing done correctly on the hair shaft does not cause biological hair thinning from the scalp, though severe chemical burns from misapplied relaxers or bleaches can scar the skin and induce traction or cicatricial alopecia.

## What you can do to manage and protect chemically processed hair

While you cannot biologically regrow broken disulphide bonds once a hair fibre exits the follicle, targeted cosmetic habits can reinforce remaining structures and prevent breakage:

1. **Space out chemical services:** Give hair at least 8 to 12 weeks between high-lift bleach or relaxer touch-ups, ensuring the chemicals are strictly applied to new growth without overlapping previously processed lengths.
2. **Incorporate dicarboxylic acid bond builders:** Cosmetic products containing maleic acid, bis-aminopropyl diglycol dimaleate, or citric acid can form temporary artificial cross-links across severed cystine chains, helping to restore tensile resistance.
3. **Balance protein and emollients:** Hydrolysed keratin and wheat proteins patch micro-gaps in damaged cuticles, while fatty alcohols (such as cetyl or stearyl alcohol) restore the lipid barrier that chemical processing strips away.
4. **Lower the washing pH:** Use shampoos and conditioners formulated near the scalp and hair's natural isoelectric point (pH 4.5 to 5.5). Mildly acidic products help close the cuticle scale and limit electrostatic swelling.
5. **Minimise thermal strain:** Keep heated tools below 180°C. High heat rapidly denatures compromised keratin, finishing off bonds that chemical treatments weakened.

## Supporting hair health from the root with Watermans

When managing hair that has endured heavy chemical processing, maintaining scalp vitality ensures that incoming new growth emerges robust and strong. 

Watermans focuses on non-invasive, nutrient-rich scalp support. Formulated with revitalising ingredients like biotin, rosemary, caffeine, and hydrolysed lupin protein, Watermans products help foster the optimal conditions for natural hair growth at the scalp level. While topical scalp formulations cannot repair disulphide bonds already severed on the lengths of your hair, keeping the scalp clean, stimulated, and nourished ensures that your next generation of hair fibres begins with the healthiest possible foundation.

## Frequently asked questions about Chemical Processing and Disulphide Bonds

### Can damaged disulphide bonds repair themselves naturally?
No, damaged disulphide bonds cannot repair themselves naturally. Hair is non-living keratinised tissue without metabolic activity, so it cannot biologically heal. Once a disulphide bond is oxidised into cysteic acid or converted into lanthionine, that specific link is permanently altered. You must rely on cosmetic bond-building agents to create synthetic cross-links, or trim away the damaged lengths as fresh, healthy hair grows from the scalp.

### What is the direct relationship between Chemical Processing and Disulphide Bonds?
The link between **Chemical Processing and Disulphide Bonds** is functional: salon chemicals are engineered specifically to break or alter these bonds. Whether reducing bonds to reform a curl pattern or unavoidably oxidising them during bleaching, every major structural or permanent colour transformation depends on altering the cortex's cystine cross-links.

### How do bond-building salon treatments interact with disulphide bonds?
Bond-building treatments use cross-linking active ingredients (such as specific dicarboxylic acids or reactive organic salts) to bridge the gap between broken, single cysteine thiol groups. While they do not recreate the identical biological disulphide bond, they create a synthetic covalent or ionic bridge that reinforces fibre stability, significantly reducing snapping during subsequent bleaching or colour services.

### Does Olaplex or generic bond builders permanently fix bleached hair?
No cosmetic bond builder permanently fixes bleached hair. Although they create strong functional bridges between broken cysteine residues, everyday shampooing, UV exposure, and heat styling gradually degrade these artificial links over time. Ongoing maintenance through bond-repair treatments and gentle hair handling is necessary to preserve hair integrity until new hair replaces the damaged sections.

## Summary of Chemical Processing and Disulphide Bonds

Navigating salon services successfully requires a clear grasp of **Chemical Processing and Disulphide Bonds**. These resilient sulphur linkages provide your hair with its natural resilience, strength, and architecture. While chemical treatments offer remarkable creative freedom to alter texture and shade, they invariably stress or permanently destroy a percentage of these structural links. By tracking porosity, avoiding chemical overlapping, employing protective bond technologies, and nurturing new growth at the scalp, you can enjoy chemical transformations while safeguarding the physical integrity of your hair fibre.

## Sources and references

- Robbins, C. R. (2012). *Chemical and Physical Behavior of Human Hair* (5th ed.). Springer-Verlag.
- Journal of Cosmetic Science. (2007). *Investigation of human hair keratin structure and changes caused by chemical treatments using Raman spectroscopy*.
- International Journal of Trichology. (2011). *Hair cosmetics: An overview*.
- Society of Cosmetic Chemists. (2018). *The chemistry of permanent waving and relaxing processes*.
- British Journal of Dermatology. (2004). *Morphological and structural changes in human hair induced by chemical treatments*.

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### Find these ingredients in Watermans products

- **Biotin**: you will find this ingredient in our [Hair Growth Shampoo](https://watermanshair.com/products/best-hair-growth-shampoo-fast-hair-growth).

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## Did you know?

- When hair is bleached, broken disulphide bonds irreversibly oxidize into cysteic acid, creating negative electrical charges that cause chronic frizz and moisture loss.
- The pungent sulfur smell produced during perming occurs because cleaving disulphide bonds releases volatile compounds like hydrogen sulphide into the air.
- Disulphide bonds make up only a fraction of hair's internal links, yet they are entirely responsible for holding its permanent structural shape and resisting water damage.


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Source: https://haircare.watermanshair.com/article/chemical-processing-disulphide-bonds