In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate.

Worldwide, iodine deficiency affects two billion people and is the leading preventable cause of intellectual disability.

This effect is due to the formation of the triiodide ion, which is brown: Iodide salts are mild reducing agents and many react with oxygen to give iodine.

Its antioxidant properties can be expressed quantitatively as a redox potential: Because iodide is easily oxidized, some enzymes readily convert it into electrophilic iodinating agents, as required for the biosynthesis of myriad iodide-containing natural products.

Iodide anions may sometimes also be found combined with mercury, copper and lead, but minerals with such compositions are even more scarce.