Iodine Disinfectants

What forms of iodine are used as topical disinfectants?

By Brian Baker

The antiseptic properties of iodine have been recognized since at least 1830, when the first iodine tincture was registered with the U.S. Pharmacoepia. The form that is active as an antimicrobial is molecular iodine (I₂). However, molecular iodine is highly reactive in its pure state and must be formulated in a way that is stable to store but is rapidly released as molecular iodine if it is to be applied topically, such as in a wound dressing or a teat dip. Various aqueous or alcoholic tinctures have been traditionally used. Iodine salts such as sodium iodide or potassium iodide are kept in solution. These remain common, but are unstable and difficult to handle in some cases. 

Complexed products are easier to handle than solutions. Non-complexed iodine is an irritant, and therefore less amenable to routine use, or as a wound dressing. The reaction product of iodine with lanolin, a natural wax from wool, is known to be an effective germicide. Glycerin is also used as an iodine carrier. More modern polymer complexes such as povidone-iodine, poloxamer-iodine, and iodine complexed with alkylphenol ethoxylates (APEs) are also used. Some APEs, such as nonylphenol ethoxylates (NPEs) have been linked to endocrine disruption. Topical use on a wound dressing might not pose a residue contamination risk, but use as a pre-milking teat dip may leave residues in the milk. 

OMRI currently maintains several categories for iodine-based disenfectants, including Iodine, LT/LH/LP (NOP); Teat Dips, LH (NOP); and Teat Dips and Udder Wash, LH/LP (COR).

This article first appeared in the summer 2009 edition of the OMRI Materials Review newsletter, and was revised in April 2022 by Senior Technical Coordinator Peter Bungum.