Good evidence
Ferulic Acid
INCI: Ferulic Acid · also hydroxycinnamic acid, the third one
A plant phenolic found in rice bran, oats and coffee, where it cross-links cell walls. In a vitamin C serum it is the ingredient that stops the other two from giving up.
Why it is here
The reason the serum has three names on the label. It stops the other two from giving up in the bottle, and in the study it doubled what they could do on skin.
Ferulic acid is itself a free radical scavenger, but its more useful role here is chemical. Added to a solution of L-ascorbic acid and alpha-tocopherol it improves the stability of both vitamins, which means more of the active survives to be applied. The measured consequence is not just longer shelf life; the photoprotection of the finished solution roughly doubles.
The receipts
Adding 0.5 percent ferulic acid to 15 percent L-ascorbic acid and 1 percent alpha-tocopherol improved chemical stability of both vitamins and doubled photoprotection against solar-simulated irradiation from 4-fold to approximately 8-fold, by erythema and sunburn cell formation.
Ferulic acid stabilizes a solution of vitamins C and E and doubles its photoprotection of skin. Journal of Investigative Dermatology, 2005. in vivo animal, n = pig skin, 4 days of application before irradiation. PMID 16185284
In normal-appearing human skin the 15 percent ascorbic acid, 1 percent alpha-tocopherol, 0.5 percent ferulic acid solution gave significant photoprotection by every measure used, including erythema, sunburn cells, thymine dimers, p53 and ultraviolet-induced cytokines.
A topical antioxidant solution containing vitamins C and E stabilized by ferulic acid provides protection for human skin against damage caused by ultraviolet irradiation. Journal of the American Academy of Dermatology, 2008. split-face, n = small; the authors list the number of patients evaluated as a limitation. PMID 18603326
In practice
- Typical use
- 0.5 to 1 percent. 0.5 percent is the studied level in the entire Duke series and the level Bright Side uses.
- Pairs with
- L-Ascorbic Acid, Vitamin E, Vitamin C + E + Ferulic
- Keep apart from
- Nothing meaningful at cosmetic levels. Its whole documented role is making other things more stable.
- Cautions
- None notable. Ferulic acid darkens over time and gives well-made vitamin C serums their faint amber cast from day one, which is different from the orange of oxidized ascorbic acid.
Questions people ask
Does ferulic acid do anything on its own?
It is a genuine free radical scavenger, and there is in vitro and animal work on it as a standalone antioxidant. But the reason it is famous, and the reason it is in Bright Side, is what it does inside the trio. The published human and animal data for ferulic acid in skincare is data on the combination.
Is ferulic acid what makes my serum smell like hot dogs?
Usually yes. Ferulic acid and its degradation products carry a distinctive savoury, slightly meaty note that gets stronger as the formula ages or warms. It is a known quirk of high-percentage C, E and ferulic serums. It is not a sign of contamination, though a serum that has also gone deep orange is past using.
Can I add a ferulic acid serum to my existing vitamin C?
Layering two finished products is not the same experiment. The stabilization happens in solution, in one formulation, at a controlled pH and ratio. Two separate products mixed on your face will not reproduce the 8-fold result. If you want that system, buy it as one bottle formulated as one system.