What is it?
A thickener and conditioning agent made from guar gum, which is ground from the seeds of the guar plant, a legume. The gum is chemically modified by reacting it with propylene oxide. It thickens and stabilizes hair and skin care products, helps condition and coat hair, is used in some hair sprays and styling products, and also appears as a gelling agent in artificial tears.
Key information
- The CIR Expert Panel concluded in 2012 that hydroxypropyl guar and related guar-based ingredients are safe as used in cosmetics.
- It is a very large molecule that is unlikely to be absorbed through the skin.
- Although its chemical definition calls it a propylene glycol ether of guar gum, the propylene glycol units are bonded to the gum, so it is not the same as free propylene glycol.
More information
Guar gum is a galactomannan, a chain of the sugars mannose and galactose stored in the seed of the guar plant. To make hydroxypropyl guar, manufacturers react the gum with propylene oxide under alkaline conditions, which attaches small propylene glycol units to the sugar chain through ether bonds. In cosmetics it is used mainly as a thickener and a hair and skin conditioning agent, and outside cosmetics it serves as a gelling polymer in an artificial tear solution.
The Cosmetic Ingredient Review (CIR) Expert Panel assessed it with 15 other galactomannans and concluded in 2012 that they are safe as used. Because the molecules are so large, the Panel judged that they would probably not be absorbed through the skin to any significant level. A leave-on styling product containing 2 percent hydroxypropyl guar produced no skin reactions in a repeated-insult patch test on 111 people. Some workers who breathe guar gum dust have developed allergies, but the Panel concluded those reports, likely due to leftover plant protein and heavy workplace exposure, were not relevant to cosmetics.
Propylene oxide, the chemical used to make it, is listed by the U.S. National Toxicology Program as reasonably anticipated to be a human carcinogen. The CIR report did not include data on leftover propylene oxide in hydroxypropyl guar and did not raise it as a concern. Hydroxypropyl guar is also different from propylene glycol, which the Foundation rates separately. On labels, it is distinct from guar hydroxypropyltrimonium chloride, a related conditioning agent the CIR also found safe.
Sources: Cosmetic Ingredient Review: Final report on the safety assessment of galactomannans as used in cosmetics (2012); National Toxicology Program: Report on Carcinogens, propylene oxide
