After an injury or getting a scare it is typical to use medical products containing iodine. They typically leave a huge red spot on the skin.

Why are creams and solutions containing iodine used in the medicine?

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    $\begingroup$ Iodine kills microorganisms, although the mechanism does not seem to be well-known: "Similar to chlorine, the antimicrobial action of iodine is rapid, even at low concentrations, but the exact mode of action is unknown." (Clin. Microbiol. Rev. 1999, 12(1), 147–179) I did see some newer research on the topic though. Some less reputable sources on the Internet write that iodine has multiple mechanisms of action, which makes it difficult for microorganisms to develop resistance. $\endgroup$ – orthocresol Jan 3 '16 at 15:06
  • $\begingroup$ @orthocresol looks like an answer to me! $\endgroup$ – jerepierre Jan 4 '16 at 17:16

This Wikipedia article gives a good, if brief, discussion of a slow-release form of iodine called "povidone-iodine" in which iodine is the only active ingredient.

Free iodine, slowly liberated from the povidone-iodine (PVP-I) complex in solution, kills eukaryotic or prokaryotic cells through iodination of lipids and oxidation of cytoplasmic and membrane compounds. This agent exhibits a broad range of microbicidal activity against bacteria, fungi, protozoa, and viruses. Slow release of iodine from the PVP-I complex in solution minimizes iodine toxicity towards mammalian cells.

PVP-I can be loaded into hydrogels, which can be based on carboxymethyl cellulose (CMC), poly(vinyl alcohol) (PVA), and gelatin, or on crosslinked polyacrylamide. These hydrogels can be used for wound dressing. The rate of release of the iodine in the PVP-I is heavily dependent on the hydrogel composition: it increases with more CMC/PVA and decreases with more gelatin.

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