Halogens are the reactive nonmetallic elements iodine, chlorine, florine and bromine.  These agents have intermediate-level disinfectant activity and can inhibit vegetative cells, cysts, endospores and most viruses.

Halogens act primarily as oxidizing agents, but can also disrupt sulfhydril groups and denature proteins.

Iodine is an effective agent against vegetative cells, cysts, viruses and endospores when used as a tincture in alcohol, but it excites pain receptors and stains clothes and skin.  Iodine mixed with mild soaps (povidone iodines such as Betadine, Wescodine and Isodine) are called iodophors and are less painful to wounds, so they are often used to help sanitize skin prior to injections or surgical incisions.

Chlorine (Cl2) is an oxidizing agent used to treat drinking water, pool water and waste water.

Sodium hypochlorite (bleach) and calcium hypochlorite (used in the dairy and food-processing industries) are chlorine-containing compounds that release hypochlorous acid when mixed with water.  Hypochlorous acid breaks down into the hypochlorite ion, however, when it comes in contact with organic matter, so these compounds have to be applied continuously to remain effective.

Chlorine dioxide is a gaseous compound used to disinfect rooms and buildings.  Chloramines are mixtures of chlorine and ammonia used to treat wounds and as mild skin antiseptics.  While these agents are milder than other forms of chlorine, they are not generally carcinogenic and release chlorine more slowly.

Bromine is used in hot tubs and as a treatment for soils, since it evaporates more slowly than chlorine, especially in higher temperatures.