Do bond builders really rebuild broken bonds? Olaplex, K18, L’Oréal and OGX, read against the chemistry

The short version

• Bleach damages the bonds that hold hair together. A 2018 study of progressively bleached hair found that oxidation targeted sulphur-containing amino acids in the cortex, “particularly the conversion of cystine disulphide bonds to cysteic acid.” [1]
• Olaplex’s patent describes formulations “for rebuilding the disulfide bonds in keratin.” [2] Its N°.3PLUS page now says the treatment works “to permanently rebuild broken disulfide bonds inside the hair.” [3]
• The independent test didn’t find that. University of Bologna researchers treated bleached hair with commercial maleate- and shikimic-acid-based “reconstructive” products. “None of the investigated treatments induced an increase in the SS disulfide bridges content of the hair cortex.” They did see smoother surfaces and better-aligned cuticle scales. [4]
• The acid treatments have better-matched data, but it’s industry data. A 2025 L’Oréal study found citric acid reinforced chemically treated hair in lab fibre tests. The authors credit calcium removal, pH and the non-covalent protein network, not rebuilt disulfide bonds. [5]

Product	Scope Grade	Why	Buy
Olaplex N°.3PLUS Hair Repair Pre-Shampoo Treatment	D	“Permanently rebuild broken disulfide bonds” isn’t what independent spectroscopy found	No verified Amazon listing
K18 Leave-In Molecular Repair Hair MaskBuy on Amazon: K18 Leave-In Molecular Repair Hair Mask (opens in a new tab)	C	Patented peptide, no published independent study of the bond claim	Buy on Amazon: K18 Leave-In Molecular Repair Hair Mask (opens in a new tab)
L’Oréal Paris EverPure Bond Repair+ Pre-ShampooBuy on Amazon: L’Oréal Paris EverPure Bond Repair+ Pre-Shampoo (opens in a new tab)	C	Citric acid has lab-fibre data, from L’Oréal itself	Buy on Amazon: L’Oréal Paris EverPure Bond Repair+ Pre-Shampoo (opens in a new tab)
OGX Repair & Protect Bond Protein Repair Pre-Shampoo	D	“Rebuilds bonds in the inner hair cortex” with no bond-building active named	No verified Amazon listing

Products we read

As an Amazon Associate, FORMUSCOPE earns from qualifying purchases. Prices live on Amazon and change often, so we don’t show them. Links never change a grade.

D-graded products get no buy link, by policy.

Our pick for most people: the L’Oréal EverPure Bond Repair+ Pre-Shampoo. It makes the most modest claim (“reinforces weak bonds”), its key acid has published fibre data, and it costs about a third of Olaplex. If you want a leave-in: K18 has the most specific technology on the label, but its bond claim still rests on the brand’s own description. Skip paying extra for the word “rebuild”.

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What “bond repair” would actually have to mean

Hair keratin’s coiled structure is held by ionic forces, hydrogen bonds, van der Waals forces and disulfide bonds. Perms and relaxers work precisely by breaking and rearranging those disulfide bridges. [6]

Bleach doesn’t just “break” disulfide bonds so they can be snapped back together. In the 2018 AgResearch–Unilever study, peroxide bleaching leached proteins from both cuticle and cortex, and the oxidation converted cystine disulfides to cysteic acid. [1] Once a sulphur atom has been oxidised that far, it is no longer half of a disulfide bond.

That gives us a clear test for any “rebuilds bonds” claim: is there evidence that disulfide content inside the fibre goes back up?

• Claimed / hero active
• Fragrance & allergens
• Conditioning & film-formers
• Everything else

Olaplex N°.3PLUS 57 ingredients

• #4 Behentrimonium Methosulfate
• #5 Bis-Aminopropyl Diglycol Dimaleate
• #8 Distearyldimonium Chloride
• #10 Behentrimonium Chloride
• #21 Quaternium-91
• #25 Hydroxypropyl Guar Hydroxypropyltrimonium Chloride
• #30 Cetrimonium Chloride
• #40 Guar Hydroxypropyltrimonium Chloride
• #43 Phenethyl Benzoate
• #47 Citric Acid
• #50 Parfum (Fragrance)
• #51 Linalyl Acetate
• #52 Linalool
• #53 Hydroxycitronellal
• #54 Alpha-Isomethyl Ionone
• #55 Citronellol

K18 Leave-In Mask 21 ingredients

• #7 Behentrimonium Chloride
• #9 SH-Oligopeptide-78
• #10 Hydrolyzed Wheat Protein
• #16 Citric Acid
• #17 Fragrance (Parfum)
• #18 Geraniol
• #19 Linalool
• #20 Hexyl Cinnamal

L'Oréal EverPure Bond Repair+ 18 ingredients

• #4 Behentrimonium Chloride
• #6 Citric Acid
• #10 Parfum / Fragrance
• #12 Polyquaternium-10
• #15 Linalool
• #16 Hexyl Cinnamal
• #17 Hydroxycitronellal
• #18 Limonene

OGX Bond Protein Repair 28 ingredients

• #5 Triticum Vulgare (Wheat) Protein
• #7 Hydrolyzed Keratin
• #12 Distearyldimonium Chloride
• #13 Behentrimonium Chloride
• #14 Polyquaternium-37
• #19 Guar Hydroxypropyltrimonium Chloride
• #26 Citric Acid
• #28 Fragrance (Parfum)

Each square is one ingredient, in label order. Original FORMUSCOPE graphic. Hover or tap a square for its name.

Each square is one ingredient in label order. Under US rules, ingredients above 1% must be listed in descending order; those at 1% or less can follow in any order, so position is a rough guide to amount, not a measurement. [7]

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Product by product

1. Olaplex N°.3PLUS Hair Repair Pre-Shampoo Treatment: Scope Grade D (Weak or undercut by formula)

The claim (olaplex.com, captured Nov 13, 2026):

“Works on a molecular level to permanently rebuild broken disulfide bonds inside the hair, while many alternatives offer only temporary, surface-level coating.”

“Clinically proven to create 3X stronger,* softer hair. It rebuilds all 3 hair bonds deep in every strand” (*after 4 uses; vs. bleached hair)

The formula (INCI, olaplex.com [3]; the brand notes ingredients are subject to change): bis-aminopropyl diglycol dimaleate sits fourth, behind water, cetearyl alcohol and a conditioning quat. The list ends with Parfum plus five named fragrance allergens (linalyl acetate, linalool, hydroxycitronellal, alpha-isomethyl ionone, citronellol) and two dyes.

Check	Finding	Effect
Study type	Patent describes the bond-rebuilding concept [2]. One independent study tested maleate-based commercial restorers on bleached hair [4]	Mixed
In-vivo vs in-vitro	Hair fibres in the lab (hair is dead keratin, so fibre tests are relevant)	–
Claim vs evidence	Independent IR/Raman spectroscopy: no increase in cortex disulfide bridges; “none of our results can be interpreted as direct evidence of the sulfa-Michael reaction/cross-linking.” Surface and cuticle improvements were seen [4]	Undercuts the headline claim
“3X stronger”, “75% stronger internal structure”	Brand figures; we found no published method or data	Unverified
Vehicle	Rinse-off conditioner base with strong cationic conditioners	Explains “softer”
Conflicts	Claims and patent are the brand’s own	Noted

Why D, not F: the Bologna study couldn’t rule out disulfide changes in the cuticle, and it tested model compounds and commercial products rather than this exact 2026 formula. So the claim isn’t flatly contradicted. But “permanently rebuild broken disulfide bonds” is a precise chemical promise, and the only independent test we found didn’t see it. No buy link (our policy for D grades).

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2. K18 Leave-In Molecular Repair Hair Mask: Scope Grade C (Plausible, thin evidence)

The claim (K18’s Amazon listing, sold by K18 Hair, captured Nov 13, 2026):

“Patented K18PEPTIDE repairs hair at a molecular level to reverse damage from bleach, color, chemical services, and heat … mimics and clicks into hair’s keratin structure to reconnect polypeptide chains and disulfide bonds”

The formula (INCI via INCIDecoder [8]): SH-Oligopeptide-78 (K18Peptide™) sits ninth, after alcohol denat, fatty alcohols and a conditioning quat. Hydrolyzed wheat protein follows. The tail lists Fragrance plus geraniol, linalool and hexyl cinnamal.

Check	Finding	Effect
Study type	We found no peer-reviewed study of SH-oligopeptide-78 on hair in PubMed	C at best
Mechanism	Plausible (peptides can bind damaged keratin), but “reconnect … disulfide bonds” is unsupported publicly	Caveat
Vehicle	Leave-in, so the peptide stays on hair (a design advantage over rinse-offs)	OK
Claim match	“Most see results after 2-3 uses” is brand wording	Unverified

Why C: nothing we found contradicts the claim, and the leave-in format is sensible. But the bond claim rests entirely on the brand’s own description.

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3. L’Oréal Paris EverPure Bond Repair+ Pre-Shampoo: Scope Grade C (Plausible, thin evidence)

The claim (Amazon listing, sold by Amazon.com, captured Nov 13, 2026):

“Strengthens all hair types, reinforces weak bonds, and reduces breakage”

The formula (INCI printed on the same listing [10]): Aqua / Water / Eau, Cetearyl Alcohol, Glycerin, Behentrimonium Chloride, Stearyl Alcohol, Citric Acid, Cetyl Esters, Sodium Citrate, Isopropyl Alcohol, Parfum / Fragrance, Phenoxyethanol, Polyquaternium-10, Polysorbate 20, Hydroxypropyl Guar, Linalool, Hexyl Cinnamal, Hydroxycitronellal, Limonene

Check	Finding	Effect
Study type	L’Oréal’s own 2025 fibre study: citric acid raised denaturation temperature 6.7–15.0%, tensile modulus 7.5–23.5% and fatigue resistance 56–124% on chemically treated hair [5]	Supports “reinforces”
Conflicts	All authors are from L’Oréal Research & Innovation [5]	Caps at C
Concentration	Citric acid is sixth, but the study’s concentration and pH aren’t printed on this pack	Can’t match dose
Claim match	“Reinforces weak bonds” is broad; the study points to calcium chelation, pH and non-covalent proteins, not disulfides [5]	Wording stretches slightly

Credit where due: this is the only product here whose wording (“reinforces”) sits close to what its published data measured.

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4. OGX Repair & Protect Bond Protein Repair Pre-Shampoo: Scope Grade D (Weak or undercut by formula)

The claim (Amazon listing, sold by Amazon.com, captured Nov 13, 2026):

“Dual-action repair technology that: 1) Rebuilds bonds in the inner hair cortex and 2) Binds to damaged sites on hair cuticle” … “3x the strength.*”

The formula (INCI on the same listing [11]): wheat protein, hydroxypropylgluconamide/hydroxypropylammonium gluconate and hydrolyzed keratin, plus conditioning quats and oils. No maleate, no named bond-building peptide, no acid treatment step.

Check	Finding	Effect
Formula vs claim	Proteins and humectants condition hair; nothing on the list is a known disulfide cross-linker	Undercuts “rebuilds bonds in the cortex”
Study type	No published data found for “3x the strength”	Unverified
Claim match	“Binds to damaged sites on hair cuticle” fits cationic conditioners	Partial

Our read: a reasonable conditioning pre-wash with an overreaching label. No buy link.

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How to read a “bond repair” label in 20 seconds

1. Find the actual bond ingredient. Bis-Aminopropyl Diglycol Dimaleate (maleate), a named peptide (SH-Oligopeptide-78), or an acid treatment (Citric Acid high on the list). If you can’t find one, the “bond” claim is conditioning.
2. Translate the verbs. “Reinforces”, “strengthens” and “protects” are modest. “Permanently rebuilds” and “reverses damage” are chemistry claims that need chemistry evidence.
3. Check the tail for fragrance allergens (Linalool, Citronellol, Geraniol, Hexyl Cinnamal) if your scalp reacts to scent.
4. The cheapest repair is prevention: fewer bleach sessions and lower heat. Nothing here un-bleaches hair.

Sources

1. Grosvenor AJ, et al. The physical and chemical disruption of human hair after bleaching: studies by transmission electron microscopy and redox proteomics. Int J Cosmet Sci. 2018;40(6):536-548. [Hair fibres · AgResearch with Unilever R&D] https://pubmed.ncbi.nlm.nih.gov/30229956/
2. Pressly ED, Hawker CJ (Liqwd Inc). US Patent 9,326,926 B2: Keratin treatment formulations and methods (granted May 3, 2016). https://patents.google.com/patent/US9326926B2/en
3. Olaplex N°.3PLUS Hair Repair Pre-Wash Treatment: product page, claims and INCI. https://olaplex.com/products/olaplex-no-3-hair-perfector (accessed Nov 13, 2026)
4. Di Foggia M, Boga C, Micheletti G, Nocentini B, Taddei P. Structural investigation on damaged hair keratin treated with α,β-unsaturated Michael acceptors used as repairing agents. Int J Biol Macromol. 2021;167:620-632. [Bleached hair · IR/Raman + SEM · academic, University of Bologna] https://pubmed.ncbi.nlm.nih.gov/33279560/
5. Zhang D, Baghdadli N, Greaves AJ. Reinforcing chemically treated human hair with citric acid. Int J Cosmet Sci. 2025;47(3):411-423. [Hair fibres · industry: L’Oréal R&I] https://pubmed.ncbi.nlm.nih.gov/39757966/
6. Gavazzoni Dias MF. Hair cosmetics: an overview. Int J Trichology. 2015;7(1):2-15. [Review] https://pubmed.ncbi.nlm.nih.gov/25878443/
7. US FDA. Cosmetics Labeling Guide (order of ingredient declaration; 21 CFR 701.3). https://www.fda.gov/cosmetics/cosmetics-labeling-regulations/cosmetics-labeling-guide (accessed Nov 13, 2026)
8. INCIDecoder. K18 Leave-in Molecular Repair Hair Mask. https://incidecoder.com/products/k18-leave-in-molecular-repair-hair-mask (accessed Nov 13, 2026)
9. K18 Leave-In Molecular Repair Hair Mask: Amazon listing (claims) and brand store. https://www.amazon.com/dp/B09HR5KSR8 · https://www.k18hair.com/products/leave-in-molecular-repair-hair-mask (accessed Nov 13, 2026)
10. L’Oréal Paris EverPure Sulfate Free Bond Repair+ Pre Shampoo Concentrate: Amazon listing (claims, INCI). https://www.amazon.com/dp/B0BCGZLKKM (accessed Nov 13, 2026)
11. OGX Repair & Protect Bond Protein Repair Pre-Shampoo: Amazon listing (claims, INCI). https://www.amazon.com/dp/B0DGZ64QD5 (accessed Nov 13, 2026)
12. Olaplex N°.3PLUS: Amazon listing (claims). https://www.amazon.com/dp/B0GHSXYY3Z (accessed Nov 13, 2026)