Guar hydroxypropyltrimonium chloride is a water-soluble, organic compound that is a derivative of guar beans. While plant derived, there is a synthetic portion to it and is biodegradable.
Although a great conditioning agent for both skin and hair, it is especially beneficial as a hair care product. Because it is positively charged, or cationic, it neutralizes the negative charges on hair strands that cause hair to become static or tangled without weighing hair down. With this you can have silky, non-static hair that retains its volume.
The Environmental Working Group (EWG's) Skin Deep is the world's largest personal care product safety guide. They rate ingredients according to their hazard score on a 0-10 scale from low to high hazard. For example, they give water a score of 0.
Accordingly they have rated Guar hydroxypropyltrimonium with a score of 1.