Trans-Aconitic acid is normally present in normal human urine and it has been suggested that is present in larger amounts with Reye's syndrome and organic aciduria.

Glutaric acid is a simple five-carbon linear dicarboxylic acid. Glutaric acid is naturally produced in the body during the metabolism of some amino acids including lysine and tryptophan. Glutaric acid may cause irritation to the skin and eyes. When present in sufficiently high levels glutaric acid can act as an acidogen and a metabotoxin.

3,4-Dihydroxymandelic acid exists in all living organisms, ranging from bacteria to humans.