Kendall -

The old stuff was "tincture of iodine." Iodine "dissolved" in alcohol.

It stings, partly because of the iodine but mostly because of the alcohol required to "dissolve" it. If you bandage a cut you've put it on, it can blister the skin. If you use it too frequently on a spot it can permanently change the skin color. Excessive use can damage your thyroid function(?) and for that reason it's sale is limited in several states. If mixed (correctly) with ammonia, it makes a dandy explosive.

The new stuff is "isodine" in which the iodine is part of a slightly more complex molecule, but is released as free iodine as the compound breaks down (more slowly). It's most commonly sold in my area as "Betadine," which I think is just a "trade name" for it.

Isodine/Betadine doesn't (in any case I've seen) sting, but is as effective as the "tincture" at killing the bugs.

Ask your local pharm shop.

John