Ferulic Acid

What is ferulic acid?

Ferulic acid is the most abundant hydroxycinnamic acid in the plant world (R). It is bound to the hemicellulose chains of unlignified primary cell walls through ester linkages, and is also polymerized with lignin, a component of the secondary cell wall, through ether bonds (R, R, R).

Ferulic acid is found in grains such as rice (R) wheat (R, R) oats (R), barley (R), rye (R) and maize (R). It is also present in coffee beans (R), hazelnuts (R), apples (R) and tomatoes (R).

Is ferulic acid stable?

The use of ferulic acid in cosmetics is hindered by its pH- and temperature-related instabilities. A low pH, a low temperature, and a high percentage of the solvent dipropylene glycol help improve ferulic acid's chemical stability (R). Attempts have been made to protect ferulic acid from decomposition using controlled release technologies. For instance, ferulic acid chemically incorporated into a polymer backbone protects it from premature degradation without compromising its antioxidant and antibacterial activities (R). In addition, the inclusion of ferulic acid with α-cyclodextrin not only improves its photostability but also slows its delivery, increasing its bioavailability in the skin (R).

Does ferulic acid get absorbed?

Ferulic acid has been shown to penetrate the skin up to a depth of at least 500 μm when incorporated in oil-in-water emulsions or gels (R). The penetration enhancer oleic acid as well as various vesicular liposomal systems can improve permeation and skin deposition (R, R). pH also impacts the permeation of ferulic acid, with faster permeation observed for a solution / gel of ferulic acid at pH 6 compared to at pH 7.4. This is thought to be due to the carboxylic moiety, which is believed to be more in the ionized form at pH 7.4 than at pH 6 (21). The non-ionized form is beneficial to skin partitioning because of its lipophilicity (R).

The transdermal penetration level of ferulic acid is relatively low; more ferulic acid is retained in the skin rather than penetrating through it (R). Transdermal absorption is further retarded by entrapping ferulic acid within niosomes (R). However, a transdermal hydrogel patch is under development (R).