Caffeic Acid

A plant polyphenol — one of the hydroxycinnamic acids — found widely in coffee, fruit, herbs and vegetables. Its close relative ferulic acid, the methyl ether of caffeic acid, is the one better known in skincare for stabilising vitamin C. In formulas it is used as an antioxidant. It is not a headline active in the way retinol or vitamin C are — it works in a supporting role, contributing antioxidant capacity and helping protect other ingredients from oxidising.

Caffeic acid donates an electron to free radicals, which stops them taking one from skin proteins and lipids. That is the basic mechanism behind every topical antioxidant. In practice, polyphenols like this one are most useful alongside other antioxidants rather than alone — different antioxidants neutralise different radical species and can regenerate one another, so combinations tend to hold up better than any single ingredient.