Bile acid

A bile acid is a steroid-derived amphiphilic compound with a carboxyl-containing side chain. Its comparatively hydrophobic ring framework and polar groups help organize otherwise poorly water-soluble lipids in an aqueous environment.

Biological conjugation can convert the acid group into an amide, changing ionization and solubility behaviour. At relevant aqueous conditions, ionized forms are often called bile salts. The number and orientation of hydroxyl groups affect the balance between polar and nonpolar surfaces, so different bile acids need not have interchangeable physical properties.