The process of histamine inactivation in biological species involves its metabolism through the oxidative deamination of its primary amino group. This reaction is catalyzed by the enzyme diamine oxidase (DAO). The metabolite produced from this reaction is imidazole-4-acetaldehyde.
Imidazole-4-acetaldehyde is then further oxidized by a NAD-dependent aldehyde dehydrogenase,  leading to imidazole-4-acetic acid.