In vitro testing documented antioxidant and anti-inflammatory activity of PCA, while liver protection in vivo was measured by chemical markers and histological assessment.

[10] In two preclinical investigations, protocatechuic acid from Hibiscus sabdariffa showed an excellent ability to effectively inhibit the replication of herpes simplex virus type 2[11] and to potently deactivate the catalytic activity of urease.

[14] The hardening of the protein component of insect cuticle has been shown to be due to the tanning action of an agent produced by oxidation of a phenolic substance.

[16] Protocatechuic acid also exists in the skins of some strains of onion as an antifungal mechanism, increasing endogenous resistance against smudge fungus.

[19] PCA is regarded as an active component in traditional Chinese herbal medicine such as Stenoloma chusanum (L.) Ching, Ilex chinensis Sims, Cibotium barometz (L.) J.Sm.