Caffeic acid, Caffeic acid, molecular formula C9H8O4, molecular weight of 180.15, from the yellow crystal in a concentrated aqueous solution, from a dilute aqueous solution of a hydrate. Decomposition point 223 ~ 225° (softened at 194°). Slightly soluble in cold water, soluble in hot water and cold ethanol. It can be used safely in cosmetics and has a wide range of antibacterial and antiviral activities. It absorbs ultraviolet light. Low concentration that is to inhibit the skin type hair dye auxiliant, is conducive to enhance the intensity of color.

On October 27, 2017, the world health organization's international agency for research on cancer released a preliminary list of carcinogens for reference, coffee acid in the 2B list of carcinogens.

Properties: yellow crystal (water), orange in alkali solution, irritant.

Density (g/mL,25/4℃) : 1.478

Melting point (° C) : 194-198

Boiling point (° C, normal pressure) : 223~225 (dec)

Flash point (° C) : 220

Solubility: soluble in hot water, ethanol, slightly soluble in cold water