Bis-aminopropyl diglycol dimaleate

What it is

• A salt of a flexible ether-diamine (1,13-diamino-4,7,10-trioxatridecane, the "bis-aminopropyl diglycol" part) with two maleate ions. The Olaplex patent describes its binding agents as maleic-acid-type groups held to a linker by ionic bonds, so the agent is "typically a salt".
• It was invented by Eric Pressly and Craig Hawker (priority 2013, patent granted 2015) and is now owned by Olaplex.
• Olaplex No. 1, the salon bleach additive, contained 9.15% of the diamine, formulated in water with maleic acid, as measured by a competitor's lab. Gargano 2018 Olaplex No. 0 lists only water, this ingredient, phenoxyethanol and sodium benzoate. Martins 2024

How it works

The claimed mechanism, from the patent: the maleate groups react with free thiol groups in hair to make carbon-sulfur covalent bonds, so a two-ended molecule could bridge two broken cysteines.

Problems with the claim:

• Bleaching oxidises cystine mostly to cysteic acid, not to free thiols, so there are few thiol targets in bleached hair. Grosvenor 2018; Kuzuhara 2006
• Because the active is an ionic salt, the maleates are not covalently tied to the diamine, so one molecule cannot form a covalent bridge as drawn in marketing (our inference from the patent's own description).
• An independent infrared and Raman study found no increase in cortical disulfides and "no direct evidence" of the claimed reaction after maleate-based treatments, though the cuticle looked more regular. Di Foggia 2021

A more plausible mechanism: the protonated diamine, with two positive charges, binds pairs of negatively charged cysteic-acid groups, like an ionic cross-link. A 2025 study called this diamine "a representative hair-rebonding compound" and engineered derivatives to reach deeper into the fibre. Kang 2025 Bleached hair surfaces carry about 2.2 such negative groups per square nanometre, so there are plenty of binding sites. Korte 2014

What the studies show

• One leave-in application of Olaplex No. 0 (10% of tress weight) raised single-fibre tensile strength of bleached hair by 47.6% versus untreated bleached hair (p < 0.05), while K18 gave +19.5% (not significant). Only 3 tresses per condition were used. A chemical test found more sulfur-linked bonds, but the Raman disulfide signal did not rise. Martins 2024
• On bleached hair treated with maleate and shikimic-acid repair products, none increased cortical disulfide content, and the cuticle looked smoother under the microscope. Di Foggia 2021
• In a competitor's lab, about 17.5% of the diamine degraded over a 40-minute model bleach (7.1% in a commercial bleach) into an azanyl ester by-product. Gargano 2018
• New thiol-reactive cross-linkers beat a reference bond builder in tensile and reactivity tests on cut hair. El Khatib 2025
• A modified version of the diamine penetrated deeper and raised the tensile strength of damaged hair. Kang 2025
• No randomised, blinded or on-head study of Olaplex or this ingredient has been published (we searched on 2026-10-10).

How it's used in studies

• Patent examples used about 3% in water, sometimes mixed 1:1 with conditioner.
• Salon use is about 1.875 mL of Olaplex No. 1 per full-head bleach service, per the product instructions cited in the Coty study. Gargano 2018
• The independent test used Olaplex No. 0 at 10% of tress weight, left on, with 48 hours of conditioning before testing. Martins 2024

Side effects and safety

• We found no specific safety assessment of this ingredient by the US Cosmetic Ingredient Review or the EU's scientific committee. Its maleic acid component is an irritant at high concentrations (see maleic acid). CIR 2007
• In bleach, the diamine partly converts to an azanyl ester whose toxicology has not been published. Gargano 2018
• Olaplex controversies, which are not about this ingredient itself: in February 2023 about 30 US consumers sued Olaplex alleging hair loss and scalp blistering, naming the fragrance ingredient lilial and panthenol. Olaplex denied it. Lilial has been on the EU list of banned cosmetic ingredients since 1 March 2022. Regulation (EU) 2021/1902 We found no evidence that any Olaplex ingredient causes hair loss.
• It is sold as a cosmetic ingredient in the US, EU and UK, and is not prescription-only.

Bottom line

It suits people who bleach, highlight or high-lift colour, used as a salon bleach additive and/or a weekly at-home treatment. Use it after shampoo and before conditioner, on top of and not instead of a good cationic conditioner and heat protection. A budget alternative is an acidic conditioner with citric acid, which has comparable in-vitro support from its maker. Zhang 2025 We rate the evidence D: real strengthening on cut hair in one small independent study, a disputed mechanism and no human trials. See bond builders.

Fun facts

• A competitor's lab found almost a fifth of Olaplex's active diamine reacts with the bleach itself during a 40-minute service. Gargano 2018