Bond Repair Treatment: Does It Work, and Which Kind Do You Need?
Two words on a label can stand for several unrelated chemistries, and little of the evidence behind them is independent. If your hair has never been lightened, colored, relaxed or permed, you probably do not need one.
Direct answer
A bond repair treatment is a hair product meant to make damaged hair stronger by acting on links inside the fiber. The label names a goal, not one chemistry: acids, maleate-based actives and peptides all carry it. Independent evidence comes down to three university studies with mixed results, two on maleate-based treatments and one on protein fragments.
Key takeaways
- "Bond repair" is a marketing term: a Scopus search for it and its variants returned one research record.
- Bleach turns most broken disulfide bonds into cysteic acid, which cannot close back into a disulfide bond, and leaves fewer free thiol groups for any reconnecting chemistry to work with.
- Three independent studies, all on bleached hair, make up the evidence: two on maleate-type treatments, with mixed results, and one small study in which keratin fragments raised wet breaking force against the conditioner's own base.
- A dry strength test can flatter bleached hair. Ask whether the hair was tested wet, against the product's own base, after more than one wash, and who paid for the study.
- No bond repair product returns bleached hair to the strength of new growth, and we found no published study of how many washes a strength gain lasts on bleached hair.
What is a bond repair treatment?
The phrase covers everything from an additive mixed into lightener at the salon to a shampoo, mask or leave-on used at home. Bond builder and hair bonding treatment are everyday names for the same thing, and none of them tells you the chemistry.
When we searched the research database Scopus in October 2026 for hair together with "bond builder," "bond repair," "bonding treatment" and similar terms, it returned one record, a 2026 book chapter. The published work sits under chemical names instead: Michael acceptors, maleates, organic acids, peptides. Bond repair is a marketing category covering several unrelated chemistries.
Hair's keratin is held together by covalent disulfide bonds and by hydrogen and salt (ionic) bonds, among others; what each type does and what breaks it has its own page.
Most of the studies behind these products used chemically damaged hair, most often bleached. Normal bleaching degrades about 15 to 25% of hair's disulfide bonds, and severe lightening, such as taking black hair to light blond, as much as 45% (Robbins 2012). Bleach turns most broken disulfide bonds into cysteic acid, which cannot close back into a disulfide bond, and leaves fewer free thiol (sulfur-hydrogen) groups for any reconnecting chemistry to work with (Robbins 2012; TRI Princeton 2024). Keep that in mind when a label promises to reconnect broken bonds. The bleached hair guide covers this damage in full.
Do you need a bond repair treatment?
Only if your lengths have been chemically processed and are breaking. The studies behind these products mostly used bleached, colored, permed or relaxed hair (Martins 2024; Zhang 2025; Malinauskyte 2021; Daniels 2016), and that is the hair this article covers.
- Watch your lengths wet. On your next wash day, notice how they behave as you detangle with conditioner in. Lengths that break or stretch out when wet but seem fine dry show the pattern of disulfide loss, because wet strength follows those bonds and dry strength barely does (Robbins 2012). If they feel gummy when wet or snap at a touch, start with the gummy hair guide before choosing any product.
- List what they have been through. Look at the lengths, not the roots. Have they been lightened, even once? Relaxed, permed or dyed with oxidative color? If none of these applies, the evidence in this article does not cover your hair. Hot tools are a separate question that this article does not assess.
- Notice dryness and tangles. Rough, dry or tangly hair that rarely breaks points mostly to friction at the surface, which conditioners lower for a while by depositing on it (Weiand 2025).
- Count the time you will give it: minutes per wash, and how often you lighten or color. Choose a format you will actually use every time, as directed.
Put together: - Unprocessed lengths that do not break: you do not need a bond repair product. Conditioning handles friction and feel. - Processed lengths that break, especially when wet: the evidence covers your hair. - Gummy or snapping lengths: the gummy guide first, and gentle handling. No product returns them to the strength of new growth (Draelos 2025).
The check cannot tell you what to deal with first on lengths that are still breaking. If you landed in the second or third group, the free hair consultation is built for that question. In about a minute it asks how you color, use heat and wash, and how your hair behaves. From those answers it scores porosity and damage; you give your email, and only then does it show your Damage Profile and what to do first.
What kinds of bond repair treatments are there?
Three main kinds of chemistry carry the label: maleate-based actives, organic acids, and peptides and hydrolyzed proteins. The research literature adds a few other crosslinkers, so far tested only in industry studies. Trade sources also name lipid-based products and hydroxypropyl gluconamide, with no measurements we could open. Conditioners belong in the comparison too, because they change how hair feels, which is easy to mistake for strength.
Maleate-based actives
Maleate-based actives carry a carbon-carbon double bond. The proposed chemistry is that it adds to the sulfur-hydrogen group of a cysteine, forming a sulfur-carbon link, and some patents claim this reconstructs keratin's disulfide bridges (Di Foggia 2021; TRI Princeton 2024). The reaction needs free thiols. On hair deliberately reduced with perm chemistry, which leaves many, a related dimaleate was reported to reconnect them and make the hair stronger than untreated reduced hair; that was a perming study, not a test of a bond product (Wu 2024). Bleached hair is the harder case: it has fewer free thiols, and when the active is mixed into the lightener, TRI Princeton questions whether the reaction is likely at all, because under bleaching conditions the thiols are probably oxidized quickly (TRI Princeton 2024).
Organic acids
Most proposed acid mechanisms involve no new covalent bond. A trade-journal article, not peer-reviewed, reported that di-acids used during lightening may bridge neighboring keratin chains through salt and hydrogen bonds (Förster 2018). Other proposed routes are lowering pH (Draelos 2025; Zhang 2025) and binding calcium (TRI Princeton 2024); TRI Princeton also lists two covalent hypotheses, a Michael addition and maleic acid polymerizing on its own. In one manufacturer's study, citric acid applied after chemical treatment made hair stiffer and more resistant to repeated loading, with results that depended on the earlier damage (Zhang 2025).
Peptides and hydrolyzed proteins
These are protein fragments, and in one study their size decided how far they got. In relaxed textured hair, fragments of about 221 and 2,577 daltons reached deep into the cortex, while a 75,440-dalton protein stayed mainly on the surface (Malinauskyte 2021).
Other crosslinkers
A few chemistries aim to form new covalent links between protein chains. In one company's study, a plant polyphenol used with copper was reported to crosslink keratin, and on bleached hair it reduced swelling and scale lifting (Yoshida 2023). An itaconic-acid complex has been proposed to crosslink keratin as well, though the evidence for that mechanism is a computer simulation (Camargo 2026).
| Approach | How it is meant to work | What has been measured | Independent evidence | Where it is used |
|---|---|---|---|---|
| Maleate-based actives | Attach to sulfur-hydrogen (thiol) groups in keratin, as patents and TRI Princeton describe | Dry strength of bleached fibers rose after one leave-on use; the disulfide signal did not. Spectroscopy found no rise in cortex disulfides | Two university studies, with mixed results | In the lightener and as after-care |
| Organic acids | Mostly salt- and hydrogen-bond bridges, lower pH, calcium binding | Stiffness and fatigue resistance rose after an acid treatment, in one manufacturer's study; pH alone left breaking strength unchanged | None found | In the lightener; acidic after-care |
| Peptides and hydrolyzed proteins | Small fragments enter damaged hair and bind there | On bleached hair, keratin fragments in a conditioner raised wet breaking force against the base alone; wheat and collagen fragments were not significantly better (six fibers per test). In relaxed hair, stiffness rose and breakage fell, in an industry co-funded study | One small academic study | After-care; some proteins go into the lightener |
| Other crosslinkers | New covalent links between protein chains | Less swelling and higher strength, in industry tests | None found | Lab and supplier data; one tested inside the lightener |
| Conditioning (for contrast) | Coats the surface and lowers friction | Fewer fragments in machine combing, through lower friction; the base alone did not raise breaking force | Yes, for friction | Every wash |
Not sure whether you need any of these?
Do bond builders actually work?
Some have measurably changed damaged hair in lab tests. Independent evidence is thin and mixed: one university study found a maleate-based treatment left on bleached hair raised the breaking strength of single fibers tested dry (Martins 2024), while another found no increase in disulfide bonds in the cortex after maleate-type treatments (Di Foggia 2021). A third, smaller study tested protein fragments (see keratin, below).
Both maleate studies tested less than a label promises. The Portuguese study gave bleached hair one application, left on and not rinsed, and two days later pulled about 25 single fibers to breaking, dry. The comparison was untreated bleached hair, with no test of the product's base on its own (Martins 2024). Strength rose, significantly for the maleate-based product, and a chemical thiol assay rose with it, but the Raman signal specific to disulfide bonds did not. There was no wet test and no washing.
The University of Bologna study used infrared and Raman spectroscopy on bleached hair treated with commercial products and model compounds. It found no rise in disulfide bonds in the cortex and no direct evidence of the crosslinking reaction the patents describe (Di Foggia 2021). We could read only its summary, so its bleaching conditions are unknown to us.
Why a dry test can flatter bleached hair
The missing wet test is the bigger gap, because disulfide loss shows in wet hair. In one person's frosted hair, with 48% of the disulfide bonds broken, wet strength fell by close to 60% while dry strength fell by less than 10% (Robbins 2012). An industry review reported that repeatedly bleached fibers measured stiffer than untreated ones when dry, below 60% relative humidity, and put it down to new hydrogen bonds around cysteic acid that water breaks easily (Breakspear 2024). A dry result on bleached hair needs a wet result beside it.
Some lab readings shift with pH alone. In one industry co-funded lab study, soaking bleached hair for 24 hours at pH 3 to 10 changed its calorimetry readings, swelling, water uptake and dry stiffness, but not its breaking strength, wet or dry (Malinauskytė 2020). Electron microscope images show the surface, and the contract lab TRI Princeton states that they cannot prove a bond builder has strengthened hair.
Who paid for the evidence
Most published positive results come from ingredient suppliers or brand owners, or from studies they helped fund. The one independent spectroscopy study found no direct evidence of the claimed crosslinking. That record calls for caution, not a verdict: the two maleate studies, one dry and one spectroscopic, cannot settle that question either way.
What no bond repair product can do
- Turn cysteic acid back into a disulfide bond. No product does this (Robbins 2012; Di Foggia 2021).
- Return hair to the strength of new growth. In one dermatologist's words, "None of these methods can recreate the strength of virgin, newly grown, unprocessed hair" (Draelos 2025).
- Fuse a split end. Trimming is the only way to remove one; see split ends.
- Change shedding or the scalp. For shedding, see a dermatologist.
Are bond builders permanent or temporary?
We found no published study of how long a strength gain lasts on bleached hair, so treat any gain as temporary. Martins tested one application and no washes, and Daniels a single treatment (Martins 2024; Daniels 2016). The nearest data come from one supplier's study of its own silk-protein ingredient, used during coloring: treated hair kept more resistance to breakage after five washes (Camargo 2022).
Two related points argue for caution. Surface conditioning washes off quickly in shampoo (Robbins 2012), and one dermatologist's view is that protein fragments that get inside diffuse out at the next shampoo (Draelos 2025). For maleate-based and acid treatments, we found no wash test at all.
You may also have read that bond builders "repair the molecular structure of the cuticle." No study we read shows that. In the Bologna study, treated hair looked more regular under the electron microscope, its scales overlapping more neatly, and the authors could not rule out extra disulfide bonds in the cuticle, but they found no direct evidence of the crosslinking reaction (Di Foggia 2021). In the Portuguese study, the peptide-based mask left a coating on the outside of the fiber, and the maleate-based product left the surface less regular (Martins 2024). So the cuticle claim is unproven, not disproven, and a smoother surface is not evidence of strength either.
How do you choose a bond repair treatment?
Start from your damage, then judge the claim by its chemistry and evidence:
- Confirm you need one. If your lengths are unprocessed and do not break, stop here and condition.
- Read the promise against the chemistry. A product that claims to reconnect broken bonds in bleached hair is claiming something neither study above showed (Martins 2024; Di Foggia 2021). Fewer broken pieces or easier combing is a smaller claim, and lower friction alone can deliver it.
- Find the active. Maleate-based actives (one appears on labels as bis-aminopropyl diglycol dimaleate), acids, hydrolyzed proteins and peptides are listed by chemical name. If you cannot find one, ask the maker which ingredient the bond claim rests on.
- Note the format and its contact time. A leave-on stays on the hair until the next wash, a mask for minutes, and a shampoo is rinsed out quickly. We found no head-to-head test of whether longer contact gives more benefit. What a leave-in conditioner does covers that format.
- Ask what was measured: was the hair tested wet, against the product's own base, after more than one wash, and who paid for the study? Fatigue tests, which load a fiber again and again until it fails, mimic grooming (TRI Princeton 2024). Our guide to hair tensile testing explains the methods.
- Use one system as directed. With several bond products at once you cannot tell which one, if any, is working.
- Tell your colorist what you use at home, and ask about anything added to your lightener.
On bleached hair, the gains measured above include a maleate-based leave-on (dry strength, one use), a conditioner with keratin fragments (wet strength, against its base) and, in one manufacturer's study, an acid treatment (stiffness and fatigue resistance). On relaxed hair, the peptide data come from one industry co-funded study. On rough hair that rarely breaks, the measured benefit is lower friction from conditioning.
If your lengths are lightened, colored, relaxed or permed and still breaking, the free hair consultation can show you what to do first.
What does bonding shampoo do?
A bonding shampoo cleans while carrying one of the bond chemistries above, such as an acid or a maleate-based active. It stays on the hair briefly, and shampoo surfactants wash off much of what is deposited on the surface: in one test, more than half of a conditioning polymer came off hair within a minute (Robbins 2012).
Most of the strength data above come from leave-on applications, acid treatments or conditioners rather than shampoos. One dermatologist considers rinse-off bond products less effective than leave-ons (Draelos 2025), a view no study we read has put to a direct test. If strength is your goal, ask for data on the format you will actually use.
Keratin treatment vs bonding treatment: which is better for you?
It depends on what you want. A salon keratin treatment is sold as a smoothing or straightening service, so judge it on smoothness; a bonding treatment is sold to make chemically processed hair less likely to break, so judge it on wet strength data. Protein treatments covers keratin smoothing in detail.
On an ingredient list, hydrolyzed keratin means protein fragments, and because peptides and hydrolyzed proteins are one of the main bond repair classes, many bond products are protein products too. In a small academic study on bleached hair, a conditioner containing 0.5% of these keratin fragments raised breaking force when the hair was wet, while the same conditioner base alone did not (Daniels 2016).
How often should you use a bond repair treatment, and can you overdo it?
As often as the label says: nobody has published how often a bond repair product should be used.
We found no study of bond products on intact hair, for harm or for benefit, so intact hair has no reason to use one. Some formulas leave a coating on the fiber (Martins 2024). If your hair turns stiff, coated or rough after a product, treat that as a mismatch between formula and hair: use it less often, try a lighter format, or stop.
How can you tell a bond repair treatment is working?
Feel can change at once, and that is the surface (conditioning, or an acid's effect on pH), not proof of strength. Strength, if it changes, shows in wet hair.
To track it, repeat the wet check every two weeks on the same lengths, and count the broken pieces in the comb. Count them with caution: in a 5,000-cycle machine-combing study of straight hair, friction mainly controlled how many fragments broke off, and the authors called "strength" too ambiguous a word for combing results (Davies 2026). Fewer pieces can simply mean less friction, which is still worth having.
The hair shaft is not alive, so only new growth arrives undamaged; your roots are the control. The rest of a routine for damaged lengths is in how to repair damaged hair.
Do you need to buy anything at all?
Not until the self-check says so. If your lengths are unprocessed and do not break, you can stop there.
ANATOMY is built on click chemistry, the reaction class recognized by the 2022 Nobel Prize in Chemistry. It is patented and made in Switzerland, and it was independently tested at SGS proderm in Germany, on bleached hair. None of the studies in this article tested it, which is why it is not in the table; ask of it the same questions you would ask of anything here. The Complete Reconstruction System has three steps, including the 100 ml Leave-In.
If your lengths are processed and still breaking, you can find your Damage Profile in the free consultation.
Frequently asked questions
Do bond repair products contain protein?
Many do. Peptides and hydrolyzed proteins are one of the main chemistries sold as bond repair (TRI Princeton 2024). To check a product, look on the ingredient list for hydrolyzed proteins, peptides or amino acids. If you also use a separate protein treatment, count both when you judge how your hair responds.
What is the best treatment for rebonded hair?
Rebonding is a salon chemical straightening service, so treat those lengths as chemically processed. Run the self-check on them and handle them gently while wet, when processed hair is weakest (Robbins 2012). Ask your stylist before adding a bond product between services; no study we read tested bond products on rebonded hair.
Should you use a bond repair treatment before or after coloring?
Both happen: some additives go into the lightener, and others are used at home afterward. No study we found measured whether a bond product keeps color from fading, so treat color claims with caution. Does coloring damage hair? covers the service itself.
What is the difference between salon and at-home bond treatments?
One clear difference is timing. At the salon, some bond additives are mixed into the lightener. In manufacturers' lab tests, some reduced measured damage, but whether the hair lifted as far was not reported (Camargo 2026; Camargo 2022). At home they come as shampoos, conditioners, masks and leave-ons. No study we found compared the same active used both ways.
Does bond repair help heat-damaged hair?
There is little to go on here. Most studies behind this article used bleached, colored, permed or relaxed hair, and the article does not assess heat damage. Heat damage has its own guide: heat-damaged hair.
Is bond repair suitable for curly or fine hair?
Choose by processing history rather than curl pattern or thickness. One peptide study used relaxed textured hair and found mid- and high-weight peptides made fibers stiffer and less prone to breaking (Malinauskyte 2021). A combing study on straight hair expected curly hair to behave differently (Davies 2026). No study we read compared fine hair with coarse.
References
- Robbins CR (2012). Chemical and Physical Behavior of Human Hair, 5th edition. Berlin, Heidelberg: Springer Source
- Breakspear S, Nöcker B, Popescu C (2024). Chemical bonds and hair behaviour—A review. International Journal of Cosmetic Science 46(5):806-814. Kao Germany Source
- Di Foggia M, Boga C, Micheletti G, Nocentini B, Taddei P (2021). Structural investigation on damaged hair keratin treated with α,β-unsaturated Michael acceptors used as repairing agents. International Journal of Biological Macromolecules 167:620-632. University of Bologna; no competing interests declared Source
- Martins E, Castro P, Ribeiro AB, Pereira CF, Casanova F, Vilarinho R, Moreira J, Ramos ÓL (2024). Bleached hair as standard template to insight the performance of commercial hair repair products. Cosmetics 11(5):150. Universidade Católica Portuguesa and University of Porto; European Regional Development Fund project supported by Amyris Bio Products Portugal Source
- Camargo FB Jr, Goshiyama AM, Oliveira GFD, Rossan MR, Princival CR, Katekawa E, Magalhães WV, Zito RA, Kakuda L, Maia Campos PMBG (2026). Protective and restorative effects of a bio-based crosslinking complex on chemically damaged hair. Cosmetics 13(1):3. Chemyunion with the University of São Paulo Source
- Camargo FB Jr, Minami MM, Rossan MR, Magalhães WV, Ferreira VTP, Maia Campos PMBG (2022). Prevention of chemically induced hair damage by means of treatment based on proteins and polysaccharides. Journal of Cosmetic Dermatology 21(2):827-835. Chemyunion with the University of São Paulo Source
- Zhang D, Baghdadli N, Greaves AJ (2025). Reinforcing chemically treated human hair with citric acid. International Journal of Cosmetic Science 47(3):411-423. L'Oréal Research & Innovation Source
- Malinauskytė E, Cornwell PA, Reay L, Shaw N, Petkov JT (2020). Effect of equilibrium pH on the structure and properties of bleach-damaged human hair fibers. Biopolymers 111(11):e23401. TRI Princeton with Lonza Source
- Malinauskyte E, Shrestha R, Cornwell PA, Gourion-Arsiquaud S, Hindley M (2021). Penetration of different molecular weight hydrolysed keratins into hair fibres and their effects on the physical properties of textured hair. International Journal of Cosmetic Science 43(1):26-37. TRI Princeton with Croda Source
- Daniels G, Nicholson S, Grant-Ross P, Tamburic S (2016). An ex vivo comparison of the tensile-strengthening properties of protein derivatives on damaged hair. IFSCC Magazine (3):1-6. London College of Fashion Source
- Davies T, Wortmann G, Wortmann FJ (2026). Cyclic combing of untreated and bleached human hair: analysis of the time-dependent breakage of hair through recording the formation of fibre fragments. International Journal of Cosmetic Science 48(2):201-210. Davies works for Bossa Nova Vision, which makes the combing instrument; the Wortmanns are declared industry consultants Source
- Wu Y, Ma L, Chen T, Chang K, Wang J (2024). Reconnection of cysteine in reduced hair with alkylene dimaleates via thiol-Michael click chemistry. International Journal of Cosmetic Science 46(3):457-467. Jiangnan University with Guangzhou Degu Personal Care Products Source
- Weiand E, Rodríguez-Ropero F, Roiter Y, Angioletti-Uberti S, Dini D, Ewen JP (2025). Understanding and controlling the friction of human hair. Advances in Colloid and Interface Science 345:103580. Imperial College London with Procter & Gamble Source
- Cornwell P, Cranwell P, TRI Princeton (2024). Bond Builders: Top Tips for Product Development & Must-Knows for Claim Support. 24 November 2024. Expert commentary, not peer-reviewed Source
- Draelos ZD (2025). Examining bond-building hair care treatments. Dermatology Times 46(8), 29 August 2025. Expert commentary, not peer-reviewed Source
- Förster T, Hippe T, Knübel G (2018). Is repair of lightened hair feasible? Myths and facts on different hair bonding treatments. SOFW Journal (3). Trade journal, not peer-reviewed; author affiliations not stated on the page we read Source
- Yoshida M, Maruyama R, Yamauchi A (2023). Repairing bleach-damaged hair by treating with polyphenol in the presence of Cu(II) ions. Journal of Cosmetic Science 74(3):143-157. Milbon, with the third author at the Osaka Research Institute of Industrial Science and Technology Source