Nitrites are salts and esters (R-O-N=O, R = organic residue) of the nitrous acid H - N = O2. The esters of nitrous acid (also known as nitric acid esters) are to be distinguished from the isomeric "nitro compounds". In these the organic residue is directly bound to the nitrogen atom (R-NO2).
Nitrites and nitrates are permitted as food additives in Europe under E 249 - E 252. They are mainly added to meat, as their addition preserves the fresh, red colour of the meat. Systemically they have a vasodilatory effect. They can lead to headaches, exanthema and gastrointestinal complaints.