How does iodine prevent infection?

Back off with that Bactine. “Nyet” to your nifty Neosporin too, I like good old-fashioned iodine. Sure it stings, but the stuff works great and doesn’t smear or sweat off.

So, how does it work? Also, what’s a “Tincture”? And how do they keep a heavy metal suspended in alcohol without it settling to the bottom of the bottle?

Iodine has antiseptic qualities like many other substances and at the same time is low enough in toxicity to use in small quantities on the skin. The exact mechanism it kills them with is beyond my ability to comprehend or impart.

A tincture, in medicine, is simply an alcohol solution of a medicine though other solvents may be used and still be refered to as tinctures. Perhaps someone with a better chemistry background will come in to explain this better but dissolved is different from suspended. A certain amount of iodine will evenly disperse in alcohol and not settle out until the amount of iodine reaches the saturation point. This is the same reason why the atmosphere isn’t made up of bands of gasses with the heaviest at the surface.

That’s from this microbial control page.

In this context, Merriam-Webster defines “tincture” as

I suspect that tincture of iodine is a colloidal suspension, a very opaque description of which can be found here, but I’m not sure.

Tincture of Iodine is just Iodine dissolved in ethanol.
It doesn’t form a colloid (gel) or hang in suspension or anything fancy like that. It’s prepared as a tincture. i.e. “dissolved in alcohol” because it’s much more soluble in alcohol than in water.

Tincture of iodine is OK for reducing bacteria on inanimate objects but should NOT be put on open wounds because it is just as toxic to live cells as to germs (it stings). However iodophors (complexes of iodine and a surface-active agent that releases iodine gradually and serve as disinfectant, e.g. povidone iodine) can be used on open wounds (it doesn’t sting).

Balance’s link states that alcohol does not affect viruses. I was under the impression that alcohol is also effective for viral infections. Apparently my impression is false. Will any one care to confirm or deny the efficacy of alcohol vis-a-vis viruses?

Note that not just iodine, but all of the halogens are antiseptic:

fluorine (in toothpaste),
chlorine (in bleach),
iodine (what we’re talking about),

and they’d probably even have a use for bromine (although one doesn’t come to mind–it may be too irritating to skin, but I’m sure it still has antiseptic properties).

Balance cited:

…and this is what all the halogens do. They are so incredibly reactive (in fact, halogens were the first things chemists got to react with the noble gasses; and who here doesn’t fear hydrofluoric acid?), that they essentially outcompete other ions, protiens, etc., during chemical reactions.

I’m pretty sure bromine is used in some swimming-pool purification products.

Just to clarify further, iodine isn’t a metal. It’s a halogen, as noted by Pantellerite.

Forget using tinture of iodine. They have better stuff at the store these days that feels much better, I think its called Betadine. Its very expensive though.

From Websters:
halogen
: any of the five elements fluorine, chlorine, bromine, iodine, and astatine that form part of group VII A of the periodic table and exist in the free state normally as diatomic molecules

Generally alcohol is not a reliable anti-viral agent.
However, alcoholic solutions can disrupt the structure of protein molecules. A virus may be neutralized by alcohol if it changes the shape of the viruses coat proteins. The proteins on the surface of viruses are usually pretty resistant to such environmental factors, but not always.

toadspittle is correct. Bromine is used in some swimming pool treatments, as an alternative to chlorine. It works quite well, and isn’t as sensitive to fluctuations in other chemical characteristics (pH, calcium level, etc) in the water. It gives the water a bitter taste and a soapy feel in high concentrations.

Barbitu8, I looked into the antiviral properties of alcohol a bit and found this site, which says

I’m not sure which info to trust. I haven’t been able to find any hard data on just how effective alcohol is against viruses. It may not be very effective, just more so than the soap.

The OP’s mostly been answered, but just to elaborate on the halogen thing a bit:

“Halogen” is derived from Greek “Halo” (salt) and “Genic” (producing). Halogens react freely with metals to produce ionic halide salts, like halite (NaCl) and fluorite (CaF[sub]2[/sub]).

Also, as one proceeds down the halogen period, reactivity diminishes. Fluorine reacts with everything except N, He, Ne, and Ar. Iodine won’t react with anything Fluorine won’t react with in addition to C, O, and S. Iodine’s reluctance to readily react with C-N-O probably has something to do with why it’s safe to smear on skin, unlike F and Cl.

And, in fairness to the OPer, Inky-, although Iodine is not a metal, it is the only halogen that–under some circumstances–can be a cation and act as one.