Guar Hydroxypropyltrimonium Chloride: How Cationic Guar Conditions Hair During the Shampoo

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Guar Hydroxypropyltrimonium Chloride (CAS 65497-29-2) is a cationic polymer of plant origin. It is made by grafting quaternary ammonium groups onto guar gum, the galactomannan extracted from the endosperm of Cyamopsis tetragonoloba seeds. It carries permanent positive charges and binds by electrostatic attraction to the anionic surface of the hair. What sets it apart is that it works during the shampoo itself: on rinsing, it forms a phase with the anionic surfactants called a coacervate, which deposits on the fibre and conditions it before any conditioner is applied.

Key facts

  • Origin: galactomannan from guar seed (Cyamopsis tetragonoloba), mannose/galactose ratio of about 2:1.
  • Charge: grafted trimethylammonium groups, positive charge independent of pH (about 0.5 to 1.7 meq/g).
  • Coacervate: on dilution during rinsing it separates with the surfactants and deposits on the fibre.
  • Delivery: the coacervate carries silicones and insoluble actives onto the hair.
  • Safety: assessed as safe by the CIR; no specific restriction in Regulation 1223/2009.

It is one of the most widely used conditioning agents in professional shampoos. For Hairswiss, it is a clear example of a formulation principle that is often misunderstood: in a shampoo, the amount of polymer matters less than the moment it comes out of solution.

What is the chemical structure of cationic guar?

Guar gum is a polysaccharide made of a linear chain of β-(1→4)-linked mannose units carrying single α-(1→6)-linked galactose units. The mannose to galactose ratio is about 2:1, compared with about 4:1 for locust bean gum; this dense branching explains why guar dissolves well in cold water. The molar mass of native guar gum often exceeds 2 million g/mol.

To make it cationic, the hydroxyl groups of the polymer are reacted with 2,3-epoxypropyltrimethylammonium chloride. The result is 2-hydroxy-3-(trimethylammonio)propyl ethers, with chloride as the counter-ion. The degree of substitution stays low, less than one substituent per sugar unit, and it sets the charge density of the polymer.

  • Charge density of cosmetic grades: about 0.5 to 1.7 meq/g;
  • average molar mass: from about 50,000 g/mol to over 2 million g/mol depending on the grade;
  • positive charge independent of pH, because the quaternary nitrogen does not deprotonate.

These two parameters, charge and size, determine how the polymer behaves in the shampoo and on the fibre.

Why does a cationic polymer bind to hair?

Keratin has an isoelectric point close to pH 3.7. At shampoo pH (usually 5 to 6), the hair surface therefore carries a net negative charge. This charge increases on bleached or coloured hair, because oxidation of cystine produces cysteic acid, with sulfonate groups (–SO3⁻). The mechanism is the same as the one described for amino silicones and amodimethicone: the most damaged areas attract cationic molecules more strongly.

Cationic guar does not penetrate the fibre. Its size keeps it on the surface, where it forms a thin film that reduces friction between hairs, lowers static and makes wet hair easier to detangle.

What is a coacervate and why does it form on rinsing?

In the bottle, cationic guar and anionic surfactants (Sodium Laureth Sulfate, Ammonium Lauryl Sulfate) coexist in a clear solution: the micelles, in large excess, keep the polymer-surfactant complexes dissolved. When rinse water dilutes the shampoo, the surfactant concentration drops and the balance shifts. Polymer and surfactants associate into less soluble complexes, which separate as a polymer-rich phase: the coacervate.

This only happens within a specific dilution range, the “coacervation window”. A study presented at the IFSCC 2022 congress observed it between 1:3 and 1:8 dilutions for a shampoo containing 0.25% cationic guar, while the window with Polyquaternium-10 was much narrower. Other work published in the Journal of Cosmetic Science uses a 10:1 water to shampoo dilution to simulate rinsing and shows, under the microscope, the coacervate attaching to the fibre in flowing water.

The coacervate has a second role: it traps insoluble actives dispersed in the shampoo, such as dimethicone droplets, and carries them onto the hair. This is how a “2-in-1” shampoo manages to deposit a silicone even though it is designed to cleanse.

Which formulation factors change its performance?

  • Charge density. High charge gives a more compact, more substantive coacervate; low charge gives a more fluid coacervate and a lighter feel.
  • Molar mass. High molecular weight grades condition more; shorter grades are chosen for fine hair, which they weigh down less.
  • Surfactant system. The type and amount of surfactants set the position of the coacervation window. Amphoteric co-surfactants such as Cocamidopropyl Betaine and salt change the charge of the micelles and therefore deposition.
  • Concentration. In shampoos, cationic guar is used at fractions of a percent: it works through targeted deposition, not quantity.

Like any cationic polymer, it can build up on fine or low-porosity hair if the same highly conditioning formula is used every time. An occasional clarifying shampoo removes these deposits.

How does it differ from Polyquaternium?

Polyquaternium grades are either synthetic polymers (Polyquaternium-6, -7, -22) or cationic cellulose derivatives (Polyquaternium-10). Cationic guar belongs to the same functional family, but its backbone is a natural galactomannan. Its wide coacervation window makes it a robust polymer: it deposits over a broader range of dilutions, so it is less sensitive to how much water is used at the backwash. Many formulas combine both types to balance detangling and lightness.

Is Guar Hydroxypropyltrimonium Chloride safe?

The Cosmetic Ingredient Review (CIR) assessed sixteen galactomannans, including Guar Hydroxypropyltrimonium Chloride, and concluded in 2012 that they are safe in the present practices of use and concentration. Their molecular size makes significant skin penetration unlikely. The ingredient has no specific restrictions under Regulation (EC) No 1223/2009.

Which professional shampoos use cationic guar?

Cationic guar is found in many professional formulas distributed in Switzerland. INEJ Remedy Shampoo by Code Zero, available on cliCHair.ch, is a classic example: Sodium Laureth Sulfate, Cocamidopropyl Betaine and Guar Hydroxypropyltrimonium Chloride are among its first ingredients, a system designed to form a coacervate on rinsing while keeping the roots of oily hair light.

For coloured hair, which is more anionic and so more receptive to cationic deposition, INEJ Color Protect Shampoo, also available on cliCHair.ch, pairs Ammonium Lauryl Sulfate with cationic guar, together with camellia and hemp seed oils.

Key takeaways

Guar Hydroxypropyltrimonium Chloride is a natural galactomannan made cationic. It stays dissolved in the shampoo, then separates on rinsing as a coacervate that deposits on the negatively charged areas of the fibre and carries other conditioning actives with it. Charge density, molar mass and the surfactant system around it determine how strongly it conditions. For professionals, this explains why the same shampoo behaves differently depending on hair porosity and on how the hair is rinsed.

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