Synthetic phenyl Acetic acid is a white crystalline compound with a honey like odour in low concentrations, used in some perfumes and in penicillin G production. In its pure form it is harmful by ingestion, inhalation or through skin contact and is a severe eye, skin and respiratory irritant. It may act as a teratogen. Naturally occurring phenylacetic acid is derived via enzymatic activity from phenylethylamine and is an abnormal product of phenylalanine catabolism, appearing in the urine in phenylketonuria.