Cosmetic chemists have questions. This new column provides answers for the budding formulator and the veteran chemist alike. This month, I give formulation advice related to guar gum in body wash and other personal cleanser formulations. If you have a formulation question, email me at [email protected].

Dear Valerie: I want to use a cationic guar gum in a body wash, but I’m not sure which one is best. We have a few coded in our lab and I’—DECISIONS DECISIONS

Dear Decisions Decisions: Cleansing formulations can benefit substantially from a cationic guar gum. Not all gums are created equal when it comes to molecular weight and cationicity, so choosing the right grade for your body wash is something to carefully consider.

Guar hydroxypropyltrimonium chloride is formed from guar gum, a polysaccharide mechanically extracted from the endosperm of a legume, the guar bean.¹ It undergoes hydrolysis and further chemical synthesis to create varying molecular weights and become cationically charged, forming guar hydroxypropyltrimonium chloride. The varying molecular weights impact skin and hair feel, as well as end specifications of a formulation. The cationicity will determine how substantive the gum is to skin or hair, which impacts performance.

When looking for the right cationic guar gum, first narrow down which ones work best in the system you are formulating. Is your body wash going to be opaque or transparent? The technical data sheet will indicate for which system it is appropriate. Don’t forget to review whether or not the gum requires neutralization or has special considerations for processing. Next, I would consider substantivity. In hair care, the cationicity of quaternized guar gum is incredibly important because damaged hair tends to be negatively charged. This allows the positively charged guar gum to deposit onto the hair, providing a conditioned feel. It can also help deposit other water-insoluble ingredients, like silicones or oils. While skin tends to be less anionic than hair, the substantivity principle still applies. Molecular weight will also be something to note as molecular weight plays a role in the sensorial properties. I don’— SINGLE OR MINGLE

Dear Single or Mingle: Any surfactant can technically be used on its own, but the question would be better phrased as whether or not it should be used alone.

Disodium cocoamphodiacetate is an amphoteric surfactant generally used as a secondary surfactant. This means it is not usually used alone or at the highest surfactant level in a formulation. Disodium cocoamphodiacetate works best as a secondary surfactant because of its exceptional mildness and contribution to foaming properties. When used in conjunction with anionic surfactants, it synergistically thickens the formula. I personally reach for disodium cocoamphodiacetate when I need higher viscosity and excellent flash foam with compact bubbles.

While surfactants like disodium cocoamphodiacetate can be used alone (one supplier recommends it to be used alone in moist wipes), multiple surfactants of varying chemistries are needed to achieve optimum cleansing, flash foam, foam profile, formula rheology and rinseability. I liken it to a performing artist singing a melody. The song feels more complete when supported by the subtle background voices singing the harmony. This is much like how a primary surfactant is complemented by the benefits of secondary surfactants. They give your overall formula properties it would not have if you just used the primary surfactant alone.

Another reason why disodium cocoamphodiacetate is better used as a secondary surfactant, is because it can aid in the solubilization of other solid surfactants, like sodium cocoyl isethionate (SCI). SCI is notoriously difficult to solubilize and keep solubilized. Because of its amphoteric character, disodium cocoamphodiacetate helps improve the solubility of SCI during processing, which in turn helps prevent the precipitation of SCI during product stability.²

Of course, the quickest way to determine whether or not you should use this surfactant alone is to try it out on the bench and see how you like the cleansing capabilities it offers throughout the entire experience, from dispensing to lathering to rinsing. 

References:

1. Mudgil, Deepak et al. “Guar gum: processing, properties and food applications-A Review.” Journal of food science and technology vol. 51,3 (2014): 409-18. doi:10.1007/s13197-011-0522-x
2. Sun, James Ziming et al. “Solubilization of sodium cocoyl isethionate.” Journal of cosmetic science vol. 54,6 (2003): 559-68.