Guar and its derivatives are used in many shampoos, conditioners, and styling products. These ingredients always seemed pretty innocuous to me, so I was surprised when I found a few curlies who did not like the performance of products that contained them. It seemed like a good idea to put on my scientific detective cap and delve more deeply into the topic of guar and its derivatives, such as guar hydroxypropyltrimonium chloride.

What is Guar?

Guar gum is a naturally occurring biopolymer obtained from the seeds of the guar plant (Cyampopis tetragonolobus,). Grown in semi-arid regions, this biopolymer belongs to a specific group of polysaccharides known as galactomannans. Guar is a water-soluble polymer due to the presence of many hydroxyl (-OH) groups along its backbone.

The guar plant

Depending upon its concentration, guar can thicken an aqueous solution considerably, and also has the ability to form gels. For this reason it is often used in shampoos, conditioners, and hair gels as a viscosity modifier (thickener). It also has the property of being shear-thinning, which means its viscosity decreases when mechanical shear is applied. The result is that the product can be poured or squeezed out of the container with little force, but it comes out slowly enough to be thick and luxurious. Application to the hair feels smooth and silky, as the shear forces applied allow for easy spreadability. For these reasons, guar is often found in foods as well, such as ice cream, where it increases the viscosity and improves the texture.

Hydroxypropyl Guar

This is a derivative of guar that has been hydrophobically modified by the addition of hydrophobic moieties along the

Figure 1. Chemical structure of guar, source: Martin Chaplin BSc PhD, http://www.lsbu.ac.uk/water/hygua.html

backbone of the polymer. The typical degree of substitution is not very high because it is undesirable that the molecules become insoluble in water. The addition of these few hydrophobes along the polymer allows it to work as an even more efficient thickener via a mechanism known as hydrophobic interaction. Products using this polymer at very low concentrations are relying upon its ability to provide excellent texture and viscosity modification.

What is guar hydroxypropyltrimonium chloride?

Guar hydroxypropyltrimonium chloride (INCI name), also known as 2-hydroxy-3-(trimethylammonium)propyl ether chloride by strict organic nomenclature, is a quaternized derivative (cationically modified) version of the guar polymer. This high molecular weight polymer retains its original structure, but has side groups added along the backbone of the chain that possess a positive charge.

This cationic polymer has all of the thickening capabilities of the original guar gum, but also has the additional benefits of substantivity to keratin (hair protein,) and improved moisture retention, as well as improved wet and dry compatibility. It has also been found to decrease irritation when used in body washes and shampoos which contain certain anionic surfactants that are known irritants. Another benefit of cationic conditioners is that they tend to resist buildup. They are used at relatively low concentrations in formulations (see Table 1 below,) because not very much is necessary to achieve the desired effects.

Figure 2. Chemical structure of Guar hydroxypropyltrimonium chloride, courtesy Hercules Incorporated, Aqualon Division

So why do some folks dislike this ingredient?

The reason some curly haired consumers dislike guar and its derivatives may be the same reason others enjoy it. The presence of so many hydroxyl (-OH) groups along the polymer chain makes it very water soluble, but also makes it an excellent humectant. It can attract water to the hair and retain large quantities of it. In some climates and for some hair, this is a highly desirable trait.

But for other hair types and for those living in hot, humid climates, it can result in frizzy hair with a coarse texture. As with most ingredients, it is necessary to experiment with products to find what works best for your own hair.