The Science of Hair Repair

The Science of Hair Repair: Understanding Bonds and Breakthrough Ingredients

Hair damage is a common concern, whether from heat styling, chemical treatments, or environmental factors. To effectively repair and strengthen hair, it’s essential to understand the underlying structure of hair and the types of bonds that maintain its integrity. This guide explores the science behind hair bonds and the innovative ingredients that help restore hair health.

  

Understanding Hair Bonds: The Foundation of Hair Strength

Hair is primarily composed of keratin proteins, which are held together by three main types of bonds:

 

1. 

Disulphide Bonds (Covalent Bonds)

  

• Strength & Stability: These are the strongest bonds in hair, providing structural integrity and determining hair’s natural shape.
• Damage Factors: Chemical treatments like bleaching and perming can break these bonds.
• Repair Approach: Rebuilding disulfide bonds requires specific chemical agents that can reform these covalent links. 

 

2. 

Hydrogen Bonds

 

• Flexibility & Styling: Weaker than disulfide bonds, hydrogen bonds are responsible for hair’s flexibility and are easily broken by water and heat.
• Temporary Changes: These bonds reform as hair dries, allowing for temporary styling changes. 

  

3. 

Ionic (Salt) Bonds

 

• pH Sensitivity: Formed between acidic and basic side chains of amino acids, these bonds are sensitive to changes in pH levels.
• Role in Hair Health: They contribute to the overall strength and elasticity of hair.

 

Key Ingredients in Hair Repair Treatments

  Advancements in hair care have led to the development of various ingredients targeting specific types of hair damage:

 

1. Bis-Aminopropyl Diglycol Dimaleate (Olaplex)

 

• Function: Specifically targets and rebuilds broken disulfide bonds within the hair shaft.
• Benefits: Restores strength, structure, and integrity to severely damaged hair.

 

2. Maleic Acid

  

• Function: Reinforces weak ionic and hydrogen bonds, stabilising the hair’s internal structure.
• Benefits: Enhances hair resilience and reduces breakage.

 

3. Proprietary Molecule (Epres™)

 

• Function: Repairs disulfide bonds through a biodiffusion technology that works in wet and dry hair and continues working after application. 
• Science: While Epres doesn’t use dimaleate, it targets the same disulfide damage with a patented acid-free molecule (Epres has not fully disclosed the mechanism of action)

 

4. Sh-Oligopeptide-78 (K18 Biomimetic Peptide)

 

• Function: Mimics natural keratin structure, entering the cortex and reconnecting broken polypeptide chains, while it doesn’t rebuild disulphide bonds in the traditional sense, K18Peptide ‘clicks’ into damaged areas of the keratin structure, helping to realign and support the overall architecture of the hair, including disulphide bonds in placement within the restored protein network. 
• Benefits: Improves elasticity, strength, and resilience by repairing the protein network from within.

 

5. Citric Acid

 

• Function: Helps restore ionic bonds by lowering hair’s pH, bringing acidic and basic side chains back into interaction.
• Additional Role: Helps tighten the cuticle and improve hair’s manageability

 

6. Hydrolysed Proteins (e.g., Keratin, Wheat, Soy)

  

• Function: Larger broken down keratin structures into smaller peptides and amino acids to penetrate the hair shaft.
• Benefits: Temporarily fills in gaps in the hair cuticle, improve moisture retention, and increase elasticity. 

  

7. Peptides and Amino Acids

 

• Function: Peptides are shorter chains that have a signaling or structural mimicking role. Amino Acids serve as building blocks for keratin synthesis, aiding in the repair of the hair’s protein structure with added benefit of humectant properties.
• Benefits: Strengthen hair from within and improve overall hair health. 

 

8. Lipids and Ceramides

  

• Function: Temporarily restores the lipid layer (F-Layer) by mimicking its composition, which acts as a barrier to protect cuticle cohesion and prevent protein loss.
• Benefits: Enhance shine, smoothness, and manageability of hair. 

 

  Matching Treatments to Hair Needs

 Choosing the right treatment depends on the specific type of hair damage:

 

• For Chemically Damaged Hair: Treatments containing bis-aminopropyl diglycol dimaleate are effective in rebuilding disulfide bonds.
• For Heat-Damaged Hair: Products with hydrolysed proteins and peptides help repair the protein structure and restore elasticity.
• For Dry or Brittle Hair: Incorporating lipids and ceramides can replenish the hair’s natural oils and improve moisture retention. 
• For Weak or Fragile Hair: Amino acid-rich treatments strengthen hair fibers and reduce breakage. 

 

 

 

Product / System	Disulfide Bonds	Supports Polypeptide Chain	Salt Bonds	Hydrogen Bonds	Ionic Reinforcement	Lipid Barrier Support	Key Actives / Notes
Olaplex
(Bis-Aminopropyl Diglycol Dimaleate)	Yes (rebuilds covalent bonds)	No	Indirect	Indirect	Some	Minimal but not enough to feel effect	Patented molecule links broken disulfide bonds
K18
(Sh-Oligopeptide-78 Biomimetic Peptide)	Indirect (supports)	Yes (restores broken keratin chains)	Stabilizes via keratin network	Supports structure/stability	Indirectly	Some	Biomimetic peptide enters cortex and reconnects keratin-like structures
Epres
Biodiffusion Molecular Technology	Yes (rebuilds covalent bonds)	No	Indirect	Indirect	Minimal	Minimal	Acid free formula; continues working after drying; no rinse needed.
Redken Acidic Bonding Concentrate
(Citric Acid, Proteins)	No	Supports  (via proteins/peptides)	Yes	Yes	Yes	Some	Uses acidic pH and protein blend to support hair strength
L’Oréal Citric Acid Complex
(Citric acid + low pH)	No	No	Yes	Yes	Some	Minimal	Restores pH for ionic bond stability
Rescued By Reinforcement
(Hydrolyzed protein, citric acid, lipids)	No	Supports (protein-based support)	Yes	Yes	Yes	Yes	Strengthens ionic/hydrogen bonds + barrier; supports protein matrix with hydrolyzed proteins, low pH
Protein Treatments
(Hydrolyzed keratin, silk, soy, etc.)	No	Yes (temporary filling effect)	Yes	Yes	Yes	Minimal	Reinforces weak spots without restoring covalent chains
Conditioning Masks
(Emollients, butters, fatty alcohols)	No	No	No	Yes (moisture-based)	Minimal	Yes, strong, primary function	Improves softness, moisture, and cuticle protection

* Salt Bonds refer to the naturally occurring ionic (electrostatic) bonds within the hair protein that are pH-sensitive.
Ionic Reinforcement describes how treatments support or enhance these internal bonds by optimising pH or introducing charged molecules that interact beneficially with the hair’s structure.

Interested to see how our other Treatments in the Halo range stacked up? Visit graph on our Hair Tips Page

Combining Ingredients for Optimal Hair Repair

 Effective hair repair often involves a combination of ingredients working synergistically:

 

• Protein and Lipid Complexes: Hydrolysed proteins repair the internal structure, while lipids restore the external barrier, providing comprehensive hair restoration.
• Peptides and Ceramides: Peptides rebuild the hair’s protein matrix, and ceramides seal the cuticle, enhancing smoothness and shine.
• Amino Acids and Moisturisers: Amino acids strengthen hair fibres, and moisturisers like glycerin maintain hydration levels.

 Sum up the Science

Understanding the science behind hair structure and the function of various bonds is crucial in selecting the appropriate treatments for hair repair. By targeting specific types of damage with the right combination of ingredients, it’s possible to restore hair’s strength, elasticity, and overall health.

 

 

Sources:

1. Robbins, C. R. (2012). Chemical and Physical Behavior of Human Hair (5th ed.). Springer.
2. Olaplex Inc. – Technical Dossier & Patent Literature
3. Epres.com – Bond Repair Technology Overview
4. L’Oréal Professionnel – Citric Acid Complex Research
5. Journal of Cosmetic Science – Bonding Chemistry in Hair Fibers
6. K18Hair.com – Biomimetic Peptide Mechanism
7. Redken Education – Acidic Bonding Science
8. CosIng (EU Cosmetic Ingredient Database) – Ingredient Functions and Safety