Cinnamic acid

Cinnamic acid is a natural metabolite of cinnamaldehyde and a common balsam constituent.

Skin. A 4 percent patch test on 25 volunteers caused no irritation or sensitization. Among Peru balsam sensitized patients, 32 of 128 (25 percent) reacted to 5 percent. In 184 Japanese patients, none reacted at 2 percent and one at 5 percent.

Oral. Acute oral LD50 is 2.5–5 g/kg across rats, mice and guinea pigs; rabbit dermal LD50 exceeds 5 g/kg.

Reproductive. Oral 5 or 50 mg/kg throughout pregnancy in rats produced no embryotoxic effects. Pup weight, size, survival and development were normal. The compound did not bind to estrogen receptors in rat uterine tissue.

Liver. Does not deplete hepatic glutathione.

Mutagenicity. Non-mutagenic in the Ames test. Non-mutagenic in the SOS chromotest and Bacillus subtilis rec assay. Weak genotoxic activity in Chinese hamster ovary cells.

Cinnamic acid is generated in vivo from oxidation of cinnamaldehyde. Most is excreted as hippuric acid: 39–74 percent in dogs, cats, rats and rabbits. In humans 50–87 percent as hippuric acid and 1–6 percent as cinnamoyl glucuronide.

In mice, depending on intraperitoneal dose, 44–70 percent is excreted as hippuric acid (rising with dose) and 2.4–28.6 percent as cinnamoylglycine.

Cinnamic acid is a foundational constituent for balsamic notes and a natural auxiliary for cinnamon aromas. The compound also weakly inhibits monoamine oxidase.