. 2019 Apr;17(4):342–351. doi: 10.2174/1570159X16666180302120925

Table 2.

Physiological functions of free radicals.

Reactive Species	Formula	Physiological Function
Reactive oxygen species
Singlet oxygen	¹O₂	Inflammation Oxidative stress Aging mechanism
Superoxide anion radical	O₂•¯
Hydrogen peroxide	H₂O₂
Hydroxyl radical	HO•
Hypochlorous acid	HOCl
Peroxyl radical	ROO•	Unknown
Alcoxyl radical	RO•	Unknown
Reactive nitrogen species
Nitric oxide	NO	Immune process Cardiovascular modulation Nervous modulation
Nitroxyl	HNO
Peroxynitrite	ONOO^-
Reactive sulfur species
Hydrogen sulfide	H₂S	Synaptic transmission Cardioprotection
Persulfides	RSSH
Sulfur oxide	SO₂