Tincture of iodine or iodine tincture is an antiseptic, it is also called weak iodine solution. It is usually 2–7% elemental iodine, along with potassium iodide or sodium iodide, dissolved in a mixture of ethanol and water. Iodine tincture solutions are characterized by the presence of alcohol, and about the same amount (weight% content) of elemental iodine as iodide.
Although the mechanism of action of topical iodine is not fully understood, it is thought that the medication's antimicrobial effects may be due to the presence of the diatomic elemental form of iodine (free iodine). It is believed that iodine precipitates the proteins of the microorganisms by forming salts via direct halogenation. Approximately 90% of the iodine absorbed by bacterial cells reappears as the iodide, thus confirming oxidative interaction as the major bactericidal mechanism of topical iodine.

Antimicrobial activity is significantly affected by pH and is greater under acidic conditions.

Solutions of iodine usually contain potassium or sodium iodide to enhance solubility of iodine through the formation of polyiodide ion.

Uses

Wound Disinfectant

People began using tincture of iodine as a wound disinfectant in the late 1800s. Although not as popular today, it is still in use as an antiseptic to prevent infection in minor cuts, scrapes and burns. Tincture of iodine is suitable for topical use only and can be irritating to your skin. You should not use tincture of iodine on open wounds or if you are allergic to seafood.

Diagnostics

Your thyroid gland requires iodine to function correctly. If you or your doctor suspect iodine deficiency is causing your thyroid to function incorrectly, you can use tincture of iodine to perform a diagnostic test. To perform this test, you apply tincture of iodine to your skin in a three-inch patch and monitor the spot for 24 hours. Watch to see how long it takes the brown iodine stain on your skin to disappear and when it does, reapply the tincture of iodine. If you have adequate iodine in your system, you will not need to reapply tincture of iodine at all. If the stain disappears and you must reapply within the 24-hour monitoring period, the more often you do, the more your body is iodine deficient.

Drinking Water Disinfectant

In a situation where your water source becomes contaminated, such as during a flood or other natural disaster, you may receive instructions to disinfect water before using it for cooking, drinking or for brushing your teeth. If boiling is not an option, you can use tincture of iodine as a disinfection method. For tincture of iodine to be effective, the U.S. Environmental Protection Agency recommends you first filter the water and allow it to settle. If the water appears clear, add five drops of 2 percent tincture of iodine per quart. If the water is still cloudy, add 10 drops of tincture of iodine and then let it sit a minimum of 30 minutes before using.