A plant antioxidant used mainly to stabilize vitamins C and E. In that trio it doubled protection against UV damage in lab skin tests.
Ferulic acid is a polyphenol found in bran, seeds and many plants. Its best-known role in skincare is as a helper: added to a serum of 15% L-ascorbic acid and 1% vitamin E, it slowed the vitamin C from breaking down and doubled the formula's protection against UV-induced redness and sunburn cells, from about 4-fold to 8-fold.
On its own it has antioxidant and mild pigment-lightening activity in lab studies, but few human trials test it alone.
The key evidence is one lab-and-skin study from a single research group showing ferulic acid stabilized and strengthened a vitamin C + E serum. Evidence for ferulic acid alone on wrinkles or spots in people is sparse; reviews rely mainly on lab work.
Adding ferulic acid to a 15% L-ascorbic acid + 1% alpha-tocopherol solution improved its chemical stability and doubled its protection of skin against solar-simulated UV (from about 4-fold to about 8-fold), measured by redness and sunburn cells; thymine dimer formation was also reduced.
Reviews ferulic acid's antioxidant, anti-inflammatory and anti-pigment properties and its use as a photoprotective and brightening ingredient, noting that its tendency to oxidize limits formulation.