Carnosic acid is a natural benzenediol abietane diterpene found in rosemary (Salvia rosmarinus) and common sage (Salvia officinalis). Dried leaves of rosemary and sage contain 1.5 to 2.5% carnosic acid.
Carnosic acid and carnosol, a derivative of the acid, are used as antioxidant preservatives in food and nonfood products, where they're labelled as "extracts of rosemary" (E392).