---
title: "The Chemistry of Hair Breakage: What Happens Inside Damaged Fibres"
url: https://haircare.watermanshair.com/article/chemistry-hair-breakage
type: general
published: 2026-10-29T00:20:34.91+00:00
updated: 2026-10-29T00:20:50.548458+00:00
tags: ["hair-damage", "keratin", "damaged-hair", "hair-science", "hair-care-tips", "hair-breakage"]
image: https://opbmfthzsenmlfbbunpe.supabase.co/storage/v1/object/public/article-images/chemistry-hair-breakage-1793233241847-0oo1.png
summary: "Discover the chemistry of hair breakage. Learn how disulphide bond loss, heat, and chemical processing degrade keratin, and how to protect hair strength."
publisher: Watermans (https://watermanshair.com)
license: All rights reserved. AI assistants may summarize, quote, and link with attribution.
---

# The Chemistry of Hair Breakage: What Happens Inside Damaged Fibres

> Explore the chemistry of hair breakage: how disulphide bonds, lipid loss, and structural changes in the cortex cause snapped strands and split ends.

**Quick answer:** The chemistry of hair breakage centres on the degradation of structural proteins and chemical bonds within the hair cortex, particularly covalent disulphide cross-links, ionic salt bridges, and weak hydrogen bonds. When chemical processing, thermal stress, or mechanical friction oxidises cystine residues into cystic acid and strips the protective 18-methyleicosanoic acid lipid layer, the tensile strength of the fibre collapses. The primary limitation is that cosmetic products cannot permanently rebuild severed covalent bonds; they can only reinforce, lubricate, and patch the damaged matrix temporarily.

## Key takeaways

- Hair breakage occurs when mechanical tension exceeds the reduced tensile strength of a chemically or thermally degraded hair shaft.
- The cortex supplies over 80 percent of hair's mechanical strength, held together by disulphide bonds, salt bridges, and hydrogen bonds.
- Chemical bleaching, permanent waving, and alkaline relaxers break disulphide bonds, oxidising cysteine into cysteic acid and leaving the cortex vulnerable.
- The protective epicuticle is coated with 18-methyleicosanoic acid (18-MEA), a lipid layer that repels water and minimises friction; losing it accelerates physical fracture.
- Hair breakage is entirely distinct from follicular hair shedding and alopecia, though both can occur on the same scalp simultaneously.

## The Chemistry of Hair Breakage: what the evidence shows

The chemistry of hair breakage involves progressive molecular failure inside the hair shaft. A single human hair fibre consists of three concentric layers: the outer protective cuticle, the structural cortex, and the central medulla. The cortex contains parallel bundles of keratin intermediate filaments embedded in a high-sulphur protein matrix. This composite architecture gives hair its remarkable tensile strength, allowing healthy dry hair to stretch by roughly 20 to 30 percent before rupturing.

![The Chemistry of Hair Breakage: what the evidence shows in the context of The Chemistry of Hair Breakage](https://opbmfthzsenmlfbbunpe.supabase.co/storage/v1/object/public/article-images/chemistry-hair-breakage-1793233249195-op23.png)

```
+-------------------------------------------------------------+
| HAIR FIBRE STRUCTURE |
| |
| [ Cuticle (18-MEA Lipid Layer) ] <- Surface friction |
| | |
| [ Cortex Matrix ] <- Disulphide bonds |
| | Salt bridges |
| | Hydrogen bonds |
| [ Medulla (Core) ] |
+-------------------------------------------------------------+
```

When you examine the molecular architecture, three primary chemical bonds dictate whether a hair stretches or snaps:

1. **Covalent disulphide bonds:** Formed between adjacent cysteine amino acid residues, these covalent bonds are the most durable cross-links in the fibre. They resist water, heat, and physical stretching.
2. **Ionic salt linkages:** Formed between basic amino acids (such as lysine and arginine) and acidic amino acids (such as aspartic and glutamic acid). These bonds are pH-dependent and provide structural stability in dry hair.
3. **Hydrogen bonds:** Abundant but individually weak interactions between electrical charges on polar peptide backbones. Water easily dissociates them, which is why wet hair behaves differently under physical strain.

Under mechanical stress, healthy hair absorbs energy through the reversible uncoiling of alpha-helical keratin proteins into flat beta-sheet configurations. If the chemical cross-links in the matrix are depleted, the fibre cannot transfer stress evenly. Tension concentrates at microscopic fracture points along the shaft, causing catastrophic failure: the hair snaps.

## The molecular mechanisms: how bonds are broken

Different chemical and environmental insults target specific bonds inside the hair shaft, degrading the cortex and predisposing it to fracture.

### Oxidative degradation from bleach and colour
Bleaching agents rely on alkaline hydrogen peroxide and persulphate salts to oxidise natural melanin pigments. This oxidation is non-specific. In the process, peroxide cleaves the disulphide bonds (-S-S-) of cystine residues, oxidising them through intermediate thiosulphinates into cysteic acid (-SO3H). 

Cysteic acid introduces negative charges into the cortex matrix. These charges repel each other, creating swelling, porosity, and an inability to hold internal cohesion. Studies show heavily bleached hair can lose over 40 to 50 percent of its original cystine content, severely lowering the force required to break the fibre.

### Alkaline exposure and salt bridge disruption
The natural isoelectric point of human hair sits at roughly pH 3.67, while the surface cuticle rests comfortably between pH 4.5 and 5.5. High-pH formulations, such as chemical relaxers (pH 12 to 14) or permanent tints (pH 9 to 11), force the cuticle scales to flare open. 

This extreme alkalinity deprotonates amino groups, instantly dissolving ionic salt linkages. In hydroxide-based relaxers, disulphide bonds undergo lanthionisation, converting cystine into non-reducible lanthionine cross-links while permanently destroying roughly a third of the original structural integrity.

### Loss of the protective 18-MEA lipid layer
The virgin hair cuticle is coated with an ultra-thin layer of branched fatty acids, primarily 18-methyleicosanoic acid (18-MEA), covalently anchored to surface proteins via thioester bonds. This lipid envelope renders the hair surface hydrophobic and naturally low-friction. 

A single oxidative chemical service strips the majority of 18-MEA. Without this natural lubricant, the coefficient of surface friction increases dramatically. When you drag a comb through 18-MEA-deficient hair, the cuticle tiles chip, lift, and shear off, leaving the underlying cortex exposed to direct mechanical snapping.

### Thermal protein denaturation
Styling tools operating between 180°C and 230°C quickly vaporise free and bound water within the cortex. If wet or damp hair is heated above 100°C, internal moisture boils instantly, creating microscopic voids known as bubble hair. 

Above 190°C, the alpha-helical keratin proteins undergo irreversible thermal denaturation, melting and losing their coiled geometric resilience. The fibre becomes brittle and rigid, snapping under normal styling tension.

| Damage mechanism | Target bonds / structures | Resulting chemical change | Impact on hair fibre |
| :--- | :--- | :--- | :--- |
| **Oxidative bleaching** | Disulphide bonds | Cystine converts to cysteic acid | Increased porosity, loss of wet tensile strength |
| **Alkaline relaxers** | Disulphide bonds and salt bridges | Lanthionisation, cleavage of ionic bridges | Severe reduction in ultimate tensile strain |
| **Excessive heat (>190°C)** | Alpha-keratin helical proteins | Denaturation of secondary protein structures | Fibre brittleness, internal voids, snapping |
| **UV radiation** | Cysteine, tryptophan, tyrosine residues | Photochemical cleavage, carbonyl group creation | Surface roughness, fibre yellowing, fragility |
| **Mechanical friction** | Cuticle scales and 18-MEA lipids | Shearing of thioester-bound fatty acids | High combing friction, split ends (trichoptilosis) |

## Signs to look for: breakage versus shedding

It is essential to distinguish between hair breakage and follicular shedding. Confusing the two leads to inappropriate treatments and unnecessary worry.

![Signs to look for: breakage versus shedding in the context of The Chemistry of Hair Breakage](https://opbmfthzsenmlfbbunpe.supabase.co/storage/v1/object/public/article-images/chemistry-hair-breakage-1793233249176-ivyi.png)

- **Fibre length:** Broken hairs are usually short, uneven shards of varying lengths. Shed hairs match your overall hair length.
- **Root bulb examination:** A naturally shed hair (telogen effluvium or normal cycle) features a tiny, firm, white keratin bulb at its end. A broken hair has no bulb; both ends terminate cleanly or show fraying.
- **Physical appearance under magnification:** Broken fibres display jagged ends, split tips (trichoptilosis), or node-like swellings where the cortex has collapsed outwards (trichorrhexis nodosa).
- **Behaviour during brushing:** Broken hair snaps audibly during detangling or showers down in tiny fragments onto your shoulders and sink.

## What the evidence does not show

Cosmetics marketing frequently overstates what topicals can achieve. The chemical evidence sets clear boundaries:

- **Products cannot "fuse" split ends back together permanently.** Conditioning agents and polyelectrolyte complexes can temporarily glue split ends together via cohesive polymer films, but the bond fails as soon as the hair is washed or exposed to mechanical friction.
- **Bond-building ingredients do not return hair to a virgin state.** While maleic acid and related chemistry can create artificial bridges across some cleaved protein fragments, they do not fully restore native disulphide architecture or recover the lost 18-MEA lipid barrier.
- **[Shampoo](https://watermanshair.com/products/best-hair-growth-shampoo-fast-hair-growth) and topical oils do not cure follicular hair loss.** If your hair is falling out from the follicle due to hormonal, nutritional, or autoimmune reasons, treating the fibre's chemistry will not stop shedding.

## What you can do to prevent breakage

Understanding the chemistry of hair breakage allows you to target the root physical and chemical mechanisms:

- **Maintain a slightly acidic pH (4.5 to 5.5):** Use conditioning rinses formulated within this range. Acidic pH contracts the cuticle layer, neutralises negative surface charges, and protects ionic salt bridges.
- **Replenish lost surface lipids:** Since 18-MEA cannot regrow, apply conditioning agents containing biomimetic fatty acids, cetyl alcohol, and hydrolysed proteins that temporarily coat the hydrophobic gaps and lower combing friction.
- **Minimise oxidative chemical frequency:** Space out lightening and permanent colour sessions by at least 8 to 10 weeks to prevent cumulative cysteic acid accumulation in the cortex.
- **Control styling temperatures:** Keep heat styling tools below 175°C. Always apply heat protectants containing thermal polymers (such as dimethicone or polyquaternium compounds), which slow heat transfer into the cortex core.
- **Handle wet hair with extreme care:** Water dissociates hydrogen bonds, reducing the hair's wet tensile yield point. Detangle wet hair using wide-tooth combs, generous slip, and minimal pulling force.

## Supporting the scalp and fibre: the Watermans approach

While managing mechanical friction and chemical stress protects the external hair shaft, healthy hair begins at the follicle. A well-constructed daily regimen supports both the scalp environment and the growing fibre.

Watermans GrowMe Shampoo and ConditionMe [Conditioner](https://watermanshair.com/products/hair-growth-shampoo-conditioner-deal) are formulated to complement a breakage-prevention routine. The system incorporates hydrolysed lupin protein, biotin, rosemary extract, caffeine, and allantoin. Hydrolysed proteins deposit along micro-fissures in the cuticle, helping to even out porosity and reinforce the hair shaft against daily physical friction. Meanwhile, the balanced, non-alkaline formulation cleanses without stripping the delicate lipid balance of the scalp or raising the cuticle scales unnecessarily.

## When to seek professional advice

If you observe progressive thinning at the scalp rather than short fragments snapping mid-shaft, or if you shed more than roughly 100 hairs with visible bulbs per day for over six weeks, arrange an appointment with a registered trichologist or a dermatologist. 

Sudden diffuse shedding, patchy circular bare spots, scalp redness, burning, or scaling point toward conditions such as telogen effluvium, androgenetic alopecia, or inflammatory scarring alopecias. These are medical concerns originating deep within the follicle and require clinical diagnosis rather than cosmetic fibre management.

## Frequently asked questions about The Chemistry of Hair Breakage

### How does water affect the chemistry of hair breakage?
Water readily breaks the weak hydrogen bonds that stabilise keratin proteins in the cortex. When wet, hair can stretch up to 50 percent of its length, but its yield point drops significantly. This makes wet hair especially susceptible to plastic deformation and tearing under brushing, which is why aggressive detangling on sopping wet strands accelerates the chemistry of hair breakage.

### Can severed disulphide bonds ever truly repair themselves?
No. Once disulphide bonds oxidise into cysteic acid, the process is chemically irreversible. Cosmetic bond-builders use active cross-linking agents to form new covalent or ionic bridges between surviving fragments, but they cannot regenerate original cysteine pairings. The hair fibre is non-living tissue and lacks biological repair mechanisms.

### Why does bleaching cause hair to snap so easily?
Bleaching uses alkaline agents and hydrogen peroxide to break down melanin, but it non-selectively cleaves disulphide cross-links in the cortex. This oxidises cystine into cysteic acid, stripping 18-MEA lipids from the surface. The hair loses structural strength and friction skyrockets, leading to immediate snapping under minor tension.

### What is trichorrhexis nodosa?
Trichorrhexis nodosa is a microscopic defect where cortex fibres burst radially outward due to severe localized bond failure, resembling two paintbrushes pushed against each other. It represents an advanced physical manifestation of the chemistry of hair breakage, typically caused by chemical over-processing or repeated thermal trauma.

## Understanding breakage to protect your hair

Grasping the chemistry of hair breakage transforms how you care for your hair. Snapping strands are not an unavoidable mystery; they are the direct physical result of depleted disulphide bonds, dissolved salt bridges, stripped surface lipids, and denatured keratin proteins. By respecting the hair fibre's mechanical limits, moderating alkaline and thermal exposure, and using targeted conditioning formulations to lower friction, you can preserve the structural integrity of your hair and keep it resilient against daily stress.

## Sources and references

- Chemical and Physical Behaviour of Human Hair, Clarence R. Robbins, 5th Edition, Springer, 2012.
- Journal of Cosmetic Science, "The effect of chemical treatments on the hair cuticle and cortex", Society of Cosmetic Chemists.
- International Journal of Trichology, "Hair cosmetics: An overview", 2015.
- International Journal of Cosmetic Science, "Lipids of human hair: 18-methyleicosanoic acid and its role in hair surface properties", 2004.
- British Association of Dermatologists, "Hair breakage and cosmetic hair damage guidelines", 2021.

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## Did you know?

- Disulphide bonds are covalent chemical links that provide hair its mechanical strength, and once severed by bleach or heat, they cannot naturally rejoin.
- The hair cuticle relies on an ultra-thin surface layer of fatty acids called 18-MEA, which is stripped away by chemical processing and never regrows.
- Wet hair can stretch up to thirty percent beyond its dry length, but overstretching permanently deforms the cortex and triggers sudden breakage.


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Source: https://haircare.watermanshair.com/article/chemistry-hair-breakage