Does Olaplex Actually Repair Disulfide Bonds — or Does It Work a Different Way?

Olaplex markets itself as a bond-building hair treatment whose active ingredient, bis-aminopropyl diglycol dimaleate, is patented to re-link broken disulfide bonds in hair keratin — yet the best independent laboratory evidence to date suggests the real mechanism may be something else entirely.

That gap between the marketing claim and the measurable chemistry is worth understanding in detail, because it affects how you use the product, what results you can realistically expect, and how Olaplex compares to its growing field of rivals. The short version: the hair does get stronger, but the reason it gets stronger is still genuinely contested.

At a Glance: Olaplex vs. K18 vs. Novel Thiol Cross-Linkers

The table below summarises the key data points from independent studies and brand claims for the three most-discussed bond-building approaches.

Feature	Olaplex (bis-aminopropyl diglycol dimaleate)	K18 (biomimetic peptide)	Novel thiol cross-linkers (APA/STA, research stage)
Claimed mechanism	Re-links broken disulfide (S-S) bonds via Michael addition	Reconnects broken keratin chains via peptide bonding	Chemically regenerates disulfide bridges via thiol reactivity
Tensile strength improvement vs. bleached hair	+47.6% (independent lab test)	Lower than Olaplex in same study	APA: highest of novel agents; outperformed reference agent
Disulfide (S-S) bond confirmation	Not confirmed by Raman spectroscopy in independent study	Not confirmed	Confirmed by cysteine reactivity tests (APA, especially at higher temps)
Alternative mechanism evidence	Hydrogen/ionic bonds; water-blocking; S-R bond formation	Lipophilic conditioning layer; water-blocking	Direct thiol cross-linking confirmed in vitro
Patent basis	US20150034117 (Michael addition to S-S)	Proprietary peptide sequence	Novel synthesis (APA, STA, SAA)
Regulatory/legal status	Commercially available; patent appeal reversed 2021	Commercially available	Research/pre-commercial
Key study	Martins et al., Cosmetics 2024 (MDPI)	Same study	El Khatib et al., Pharmaceuticals 2025 (MDPI)

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What exactly is a disulfide bond, and why does it matter for hair?

A disulfide bond is a covalent sulfur-to-sulfur (S-S) linkage formed between two cysteine amino acid residues within or between protein chains. In hair keratin, these bonds are the primary source of structural strength, elasticity, and shape retention. Approximately 90–95% of the hair cortex is composed of helical keratin protein, longitudinally arrayed as intermediate filaments cross-linked by a network of disulfide bridges.

When bleach, relaxers, or repeated heat styling attack the hair shaft, they break these S-S links. The result is measurable: hair becomes more porous, more prone to breakage, and loses its ability to hold curl or wave patterns. Olaplex's own brand science pages state that "increased breakage and fragility is a sign that disulfide bonds have been broken," and the brand's OLAPLEX Complete Bond Technology™ is positioned as working at the molecular level to repair them.

That claim is the crux of the debate.

What does the Olaplex patent actually say?

The original Olaplex patent (US20150034117) describes a Michael addition reaction in which bis-aminopropyl diglycol dimaleate acts as a bifunctional crosslinker. In organic chemistry, a Michael addition is a reaction between a nucleophile — in this case, a thiol (SH) group from a cysteine residue — and an α,β-unsaturated carbonyl compound (the maleate double bond in the Olaplex molecule). The patent claims the molecule bridges two broken cysteine ends, effectively re-forming a cross-link where a disulfide bond once was.

The key distinction: the new bond formed would be a sulfur-carbon (S-C or S-R) bond, not a true sulfur-sulfur (S-S) disulfide bond. The patent does not claim to restore the original S-S chemistry; it claims to restore the cross-link function using a different bond type. This nuance is routinely lost in marketing language that simply says "repairs disulfide bonds."

Chemists Eric Pressly and Craig Hawker developed the molecule at the University of California, Santa Barbara, using click chemistry — a field for which Barry Sharpless won a Nobel Prize. Sharpless once singled out Olaplex as the most interesting company, other than his own, built on click chemistry. The scientific pedigree is genuine. Whether the mechanism survives contact with real bleached hair is another matter.

What did the independent 2024 study actually find?

A team at Universidade Católica Portuguesa and the University of Porto, led by Eva Martins, published a direct test of Olaplex and K18 on bleached hair. They used two analytical methods to probe the bond chemistry.

Raman spectroscopy measures how different bonds scatter laser light. Disulfide bonds produce a characteristic signal at 425–550 cm⁻¹. If Olaplex were forming new S-S bonds — or even new S-R bonds in meaningful quantities — the Raman signal in that region should increase relative to untreated bleached hair.

Ellman's test uses a reagent (DTNB) that reacts with free thiol (SH) groups to produce a measurable yellow colour. By running the test before and after treating hair with sodium borohydride (a reducing agent that breaks S-S bonds to release SH groups), the researchers attempted to quantify sulfur bonds available for reduction.

The headline mechanical result was striking: Olaplex-treated fibres were 47.6% stronger under tension than bleached, untreated hair — the largest improvement measured, ahead of K18. Something real is happening to the hair.

The bond-level results told a more complicated story, though. The Raman S-S signal did not increase significantly for Olaplex-treated hair. The Ellman's test did show a higher reading for Olaplex, which the researchers interpreted as evidence of new S-R bond formation. Their conclusion: Olaplex forms "non-specific S-R bonds" via Michael addition, rather than restoring true S-S disulfide bonds.

Why does Dr. Michelle Wong (Lab Muffin) dispute that conclusion?

Science communicator and cosmetic chemist Dr. Michelle Wong, who holds a PhD in chemistry, published a detailed critique of the Martins et al. study's methodology. Her objections are technical but consequential.

The Ellman's test cannot measure the bonds Olaplex claims to form. Sodium borohydride, the reducing agent used in Condition 2 of the assay, breaks disulfide (S-S) bonds — but sulfur-carbon (S-R) bonds are almost always stable to borohydride and are typically only cleaved by transition metals or free radical reactions. If the assay measures what borohydride breaks, and borohydride doesn't break S-R bonds, then the test cannot be detecting the new S-R bonds the paper attributes to Olaplex.

Wong also points out that the paper is internally inconsistent: the methods section describes the assay as measuring "disulfide bond quantification," while the results section reframes the same data as measuring "S-R bonds." These are chemically different things, and the assay cannot do both.

The two Ellman conditions are not directly comparable. Condition 1 used a gentle phosphate buffer at pH 8. Condition 2 involved shaking hair in 0.2 M sodium hydroxide (pH ~13) for 24 hours — more alkaline than a standard depilatory cream. At that pH, hair's protein structure opens up dramatically, exposing far more buried S-S bonds to the reagent. Subtracting two measurements taken under such different conditions does not yield a meaningful number.

Concentration mismatches undermine the subtraction. The two conditions used wildly different volumes of Ellman's reagent relative to the hair sample (100 µL vs. approximately 1,110 µL equivalent), meaning the colorimetric readings are effectively in different units. Subtracting them directly, as the paper does, is not mathematically valid.

Bond builders may simply block water. Wong notes that both Olaplex and K18 appear to at least partly work by sitting inside the hair shaft and blocking aqueous solutions from penetrating. Water loosens hair's protein structure. If Olaplex reduces water uptake in Condition 1 (the gentler assay), fewer buried S-S bonds become accessible to Ellman's reagent — producing a lower reading that, when subtracted from the borohydride-treated Condition 2 result, creates a larger apparent gap. This would mimic the signal of new bond formation without any new bonds actually being present.

K18's formula contains oily ingredients (cetearyl alcohol, dicaprylyl ether) that the study's own microscopy suggested form a lipophilic conditioning layer on the hair surface — another water-blocking mechanism that could produce a similar artefact in the Ellman assay.

So what is Olaplex actually doing to make hair stronger?

This is where the science is genuinely uncertain. Several non-exclusive mechanisms have been proposed.

Hydrogen and ionic bonds. Hair keratin contains many sites capable of forming weaker, non-covalent interactions. A molecule that increases the density of hydrogen bonds and ionic bonds across the protein matrix would make hair feel and behave as though it has more covalent cross-links, even without forming any new S-S bonds. This is the mechanism most favoured by independent cosmetic chemists who have reviewed the literature.

Water exclusion. By occupying space within the hair cortex and reducing the degree to which water can swell and loosen the protein network, bond builders may preserve the mechanical integrity of existing bonds rather than forming new ones.

S-R bond formation via Michael addition. The patent mechanism may be partially correct — the maleate double bond in bis-aminopropyl diglycol dimaleate can react with cysteine thiols — but the resulting S-C bond is not a disulfide, and the Ellman's assay as run in the Martins study cannot confirm or deny this chemistry reliably.

Surface conditioning. The study's SEM and AFM microscopy showed that Olaplex and K18 both alter the hair surface in ways consistent with filling in cuticle damage. A smoother, more intact cuticle reduces mechanical friction and breakage independently of any bond chemistry in the cortex.

What is clear is that Olaplex's OLAPLEX Complete Bond Technology™ produces real, measurable improvements in hair mechanical properties. The 47.6% tensile strength improvement in the Martins study is not trivial. The uncertainty is about why it works, not whether it works.

How do novel research compounds compare to Olaplex's approach?

A 2025 study published in Pharmaceuticals by El Khatib et al. synthesised three novel thiol-reactive cross-linking agents — APA, STA, and SAA — and tested them on bleached human hair. Unlike Olaplex, these compounds were designed to directly regenerate disulfide bridges through thiol chemistry, and the researchers used cysteine reactivity tests — rather than the Ellman/borohydride subtraction method — to confirm the mechanism.

The results are notable. APA demonstrated the highest efficacy of the three novel agents in restoring tensile strength and elasticity, and cysteine reactivity tests confirmed that APA could effectively re-establish disulfide bonds, particularly at higher temperatures. Both APA and STA outperformed the reference agent (which, while not explicitly named in the abstract, is consistent with a commercially available bond builder) on both tensile strength and cysteine reactivity.

This research is pre-commercial and has not been tested in consumer formulations, but it matters for two reasons. First, it demonstrates that true disulfide regeneration in hair is chemically achievable — the question is not whether it can be done, but whether existing commercial products do it. Second, it sets a benchmark against which future bond-building claims can be evaluated.

What about the legal history — does it tell us anything about the science?

Not much. The 2019 courtroom win over L'Oréal that Olaplex supporters often cite as proof the science works was reversed on appeal in 2021. Patent litigation turns on claim construction and prior art, not on whether a mechanism is scientifically accurate. A 2023 lawsuit alleging hair loss and scalp damage was dismissed on procedural grounds, with no ruling on the merits. A separate shareholder derivative settlement was still awaiting final court approval as of mid-2026.

None of these proceedings resolve the chemistry question. Courts are not equipped to adjudicate molecular mechanisms, and using legal outcomes as scientific evidence cuts both ways.

How should you read Olaplex's marketing claims?

Olaplex's brand pages describe its OLAPLEX Complete Bond Technology™ as working "on a molecular level to repair these bonds and restore hair's strength," and the professional system is marketed with specific performance figures: 68% more repair and three times stronger hair for No.3 used with No.0, and three times stronger and three times softer for No.3PLUS, launched in early 2026.

These figures come from brand-commissioned testing, the methodology of which is not publicly disclosed. The 47.6% tensile strength figure from the independent Martins study is a different measurement under different conditions and is not directly comparable to the brand's own numbers. Both sets of figures agree, at least, that the product produces a real mechanical improvement.

The claim that Olaplex specifically "repairs disulfide bonds" in the way the label implies — restoring the original S-S chemistry broken by bleach — is not confirmed by independent peer-reviewed evidence. That does not mean the claim is false; it means the evidence for it is currently insufficient. The mechanism proposed in the patent (Michael addition forming S-C bonds) is chemically plausible, but studies designed to detect it have either failed to find it or used methods that cannot distinguish it from other effects.

What does this mean for how you use bond builders?

Understanding the mechanism debate has practical implications.

Timing matters regardless of mechanism. Whether Olaplex works by forming new bonds or by blocking water and adding non-covalent interactions, applying it during a chemical service (mixed with bleach or colour, as No.1 is designed to be used) gives the active ingredient the best opportunity to penetrate the hair shaft while the cuticle is open. Post-service application (No.2, No.3) may work differently — more as a conditioning and water-blocking treatment.

Heat may matter more than the label suggests. The El Khatib et al. research found that novel thiol cross-linkers formed disulfide bonds more effectively at higher temperatures. If Olaplex's Michael addition chemistry follows a similar pattern, the heat of a salon colour service may be part of why in-salon application outperforms at-home use.

Repeated use is consistent with a non-covalent mechanism. If the primary effect were true covalent disulfide repair, you might expect a cumulative improvement that plateaus once bonds are restored. If the primary effect is water-blocking and hydrogen bonding, the benefit would be maintained only with continued use — which matches most users' experience.

Combining with other treatments makes sense. If Olaplex is not specifically targeting disulfide bonds, it is not competing with treatments that address other aspects of hair damage. Using a bond builder alongside a well-formulated conditioner for colour-treated hair addresses different layers of damage simultaneously.

Is there any test that could definitively resolve the mechanism question?

Yes, in principle. The most direct approach would be to use isotopically labelled Olaplex (with ¹³C or ³⁵S incorporated into the active molecule) and then use mass spectrometry or NMR to identify labelled fragments in the hair after treatment. If the Michael addition mechanism is correct, you would find labelled sulfur-carbon bonds in tryptic digests of the treated keratin. This experiment has not, to public knowledge, been published by either Olaplex or independent researchers.

Raman spectroscopy, as used in the Martins study, is a reasonable approach but has resolution limits when trying to distinguish between closely related sulfur bond types in a complex protein matrix. The absence of a clear S-S Raman signal increase is consistent with no new disulfide formation, but it does not rule out S-C bond formation at low concentrations.

The mechanism question remains open. The Martins study is the most rigorous independent test published to date, and its conclusion — that Olaplex forms non-specific S-R bonds rather than true disulfide bonds — is itself contested on methodological grounds by chemists like Wong. What both sides agree on is that the hair gets stronger, and that the original marketing claim of disulfide repair is not straightforwardly supported by the available evidence.

The bottom line

Olaplex is defined in its patent as a Michael addition crosslinker designed to bridge broken cysteine residues in hair keratin. The real-world performance data — including a 47.6% tensile strength improvement in the best independent study — confirms that it does something meaningful to damaged hair. What that something is, at the molecular level, remains genuinely uncertain.

The most likely explanation, based on the current weight of evidence, is that Olaplex works through a combination of mechanisms: some degree of S-C bond formation via Michael addition, water exclusion from the hair cortex, and increased non-covalent (hydrogen and ionic) bonding. True disulfide (S-S) regeneration — the kind that would show up as an increased Raman signal at 425–550 cm⁻¹ — has not been confirmed independently.

For consumers, this matters less than it might seem. A product that makes bleached hair 47.6% stronger is worth using, whatever the mechanism. For the industry, it matters considerably more: if true disulfide regeneration is the goal, the El Khatib et al. research on APA and STA suggests that compounds capable of achieving it do exist — they just are not yet in your shower.

Pairing any bond-building treatment with amino acid-rich shampoos formulated for scalp health and a heat protectant addresses the full spectrum of damage pathways that bond builders, whatever their mechanism, cannot address alone.