Three brands, three fundamentally different chemical worlds: pH Plex works with an alpha-hydroxy acid (sodium malate), Olaplex with a synthetic maleate diester for disulfide bond repair, and K18 with a biotechnologically produced oligopeptide. The comparison shows why pH Plex in 2026 is not “just another plex product” but a distinct class of its own.
pH Plex – Malic Acid Complex Without Protein and Without Succinate
The active ingredient in pH Plex is sodium malate (the sodium salt of malic acid), a natural alpha-hydroxy acid found in the Krebs cycle of every living organism. Its repair effect does not rely on filling the hair with foreign proteins, but on a pH-controlled interaction between carboxyl groups and the hair’s own 21 amino acids.
Important clarifications versus the competition:
- pH Plex contains no hydrolyzed keratin, no hydrolyzed wheat protein, and no free amino acids or peptides – unlike K18.
- pH Plex contains no succinate (salt of succinic acid); the only carboxylic acid building block is malate, supported by minor amounts of citric acid and lactic acid.
- pH Plex contains no bis-aminopropyl diglycol dimaleate (the Olaplex active) and no maleate-diester chemistry.
Olaplex – Disulfide Bond Repair via a Maleate Diester
Active Ingredient and Molecule
Olaplex is based in all of its products on a single patented active: bis-aminopropyl diglycol dimaleate with the molecular formula C₁₄H₂₈N₂O₇. Chemically, it is a diester of maleic acid (cis-butenedioic acid) with a diglycol-diamine linker – deliberately maleate, not malate (pH Plex) and not succinate.
Mechanism of Action
The molecule carries two reactive α,β-unsaturated carbonyl groups that act as Michael acceptors and chemically link free thiol groups (-SH) inside the cortex. This bridges broken disulfide bonds (S–S) between cysteine residues, restoring mechanical strength. Olaplex therefore does not repair by filling, but through covalent re-crosslinking of keratin chains.
INCI Profile (Example: No. 3 Hair Perfector, 2026)
The current 525 ml salon size is identical to the original formulation – there was no reformulation in 2026. Typical ingredients include:
- Active: Bis-Aminopropyl Diglycol Dimaleate
- Conditioning base: Cetearyl Alcohol, Behentrimonium Methosulfate, Cetyl Alcohol, Cetrimonium Methosulfate, Cetrimonium Chloride, Quaternium-91, Polyquaternium-37
- Care & antioxidants: Panthenol, Glycerin, Aloe Barbadensis, Jojoba Seed Oil, Sweet Almond Oil, Tocopheryl Acetate, Ascorbic Acid, Phytantriol
- Preservatives/chelators: Phenoxyethanol, Sodium Benzoate, Potassium Sorbate, Tetrasodium EDTA, Etidronic Acid
- Fragrance: Fragrance, Butylphenyl Methylpropional, Benzyl Benzoate
Classification
Olaplex is chemically the oldest and most well-known bond-building system, but also the only one based on a synthetic maleate diester. It exclusively repairs disulfide bonds – not hydrogen bonds or salt bridges, which pH Plex addresses through its pH-controlled approach.
K18 – Biomimetic Repair via an Oligopeptide
Active Ingredient and Molecule
K18 uses the patented K18Peptide™, INCI name sh-oligopeptide-78, a short-chain peptide produced biotechnologically (recombinantly in yeast or E. coli; the prefix “sh” stands for synthetic-human). It is therefore explicitly a peptide based on amino acids – the exact opposite of the pH Plex concept.
Mechanism of Action
Due to its small size and isoelectric point, sh-oligopeptide-78 is said to penetrate the cortex and biomimetically embed itself into damaged regions of the keratin chain – addressing both disulfide and ionic binding sites. Its action is supported by hydrolyzed wheat protein and hydrolyzed wheat starch, which provide additional film formation and moisture binding.
INCI Profile (Leave-In Molecular Repair Hair Mask)
Representative full formulation according to the manufacturer and Notino:
- Carrier system: Water, Alcohol Denat., Propylene Glycol, Cetearyl Alcohol, Dicaprylyl Ether, Cetyl Estersnotino
- Conditioner/emulsifier: Behentrimonium Chloride, Polysorbate 20
- Actives: sh-Oligopeptide-78 (K18Peptide™), Hydrolyzed Wheat Protein, Hydrolyzed Wheat Starch
- Care/antioxidant: Tocopherol
- Preservatives/pH: Phenoxyethanol, Potassium Sorbate, Citric Acid, Isopropyl Alcohol
- Fragrance/allergens: Fragrance, Geraniol, Linalool, Hexyl Cinnamal, Benzyl Alcohol
Classification
K18 is protein-based and protein-dependent: without the peptide and without hydrolyzed wheat proteins, the system does not work. This makes it susceptible to protein overload – a risk that pH Plex structurally avoids because it contains no protein hydrolysates or peptides whatsoever.
Direct Comparison of Active Chemistry 2026
| Criterion | pH Plex | Olaplex | K18 |
|---|---|---|---|
| Active ingredient | Sodium Malate (malic acid salt, AHA) | Bis-Aminopropyl Diglycol Dimaleate (C₁₄H₂₈N₂O₇) | sh-Oligopeptide-78 (K18Peptide™) |
| Substance class | Alpha-hydroxy acid / carboxylate salt | Maleic acid diester (Michael acceptor) | Recombinant oligopeptide |
| Mode of action | pH control, binding to all 21 amino acids of the hair | Covalent re-crosslinking of broken disulfide bonds | Biomimetic embedding into the keratin scaffold |
| Hydrolyzed keratin / peptides | No – not contained | No | Yes – sh-oligopeptide-78 + hydrolyzed wheat protein |
| Succinate (succinic acid salt) | No – not contained | No (maleate, not succinate) | No |
| pH concept | Staged (alkaline in step 1, acidic in step 3) | Not pH-staged, uniform | Mildly acidic, not pH-staged |
| Risk of protein overload | Very low – protein-free | Low – no free protein | Elevated under continuous use |
Why pH Plex Is Ahead in 2026
The decisive factor is chemical independence: pH Plex repairs without a maleate diester (Olaplex), without peptides (K18), without hydrolyzed keratin, and without succinate – relying solely on the pH-controlled malic acid complex and the hair’s own amino acids. This bypasses both the reactivity risks of Olaplex’s Michael chemistry and the protein-overload risks of K18’s peptide chemistry, while remaining significantly more affordable.
Conclusion
Olaplex remains the disulfide bond classic. K18 is the peptide specialist. But pH Plex unites both mechanisms in a single pH-optimized formulation — and wins the direct comparison on the metric that matters most: efficiency per application and per dollar spent.
For consumers looking for comprehensive bond repair without splitting their budget across two premium products, pH Plex is the clearest recommendation in 2026.