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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.

Taurine is 2-aminoethanesulfonic acid, an amino sulfonic acid with a two-carbon chain between its amino and sulfonic-acid groups. Around physiological pH, taurine predominantly has a zwitterion structure.

Taurine can participate in conjugation of bile acids, helping form amphiphilic molecules involved in lipid digestion. Its sulfonic-acid group distinguishes it from the carboxylic-acid amino acids incorporated into proteins.^[ref]