Choosing the best iodine solution depends entirely on the purpose for which it is intended. Iodine solutions contain elemental iodine dissolved in specific proportion to potassium iodide, or sodium iodide in water or in a water and ethanol mixture. One of the lowest strengths, the standard concentration for use of iodine as a starch indicator, is 0.3% weight to weight (w/w). The highest concentrations, up 12% povidone-iodine in water, are used as skin antiseptics in hospitals, primarily in preparation for surgery. Several levels in between are used for infection control, to treat eye infections, and even to purify water.
Infection prevention is one of the most well-known uses for an iodine solution. Betadine, most often a 10% solution of povidone-iodine in water, is a good choice for consumers to use as an antiseptic to treat minor wounds and infections. Iodine is an especially effective disinfectant as it affects a wide range fungus, bacteria, and microorganisms. This solution strength seems to be safe for most people. It can, however, cause skin irritation, stains, and allergic reactions, along with an uncomfortable stinging sensation called iodine burn.
Povidone-iodine solutions can be used to treat bacterial conjunctivitis and even common skin problems, like acne. They can also alleviate coughing symptoms. In hospitals, stronger concentrations of povidone-iodine are used not only to disinfect a patient's skin but also the surgeon's. The iodine solution works to reduce the amount of microorganisms on the doctors' and nurses' hands and forearms.
Another highly recognizable form of iodine solution is Lugol's solution, which contains 5% iodine and 10% potassium iodide, weight over volume (w/v), and no alcohol. Also used as an antiseptic in hospital settings, Lugo's solution may be a good choice for someone seeking a highly effective germicide. One disadvantage to this solution strength of iodine is that it can lead to scarring. Most medical professionals avoid this by using a solution of ethanol to wash off the iodine after treatment. In response to potential negative side effects and use in developing illegal drugs, in 2007, the U.S. Drug Enforcement Administration (DEA) began regulating Lugol's solution and any iodine solution with more than a 2.2% concentration.
Doctors have also been focusing on iodine as an essential part of the human diet. It has been linked to overall health but more specifically to thyroid function and prevention and treatment of breast cancer. As a diet supplement, iodine is not taken in solution but in solid form, like a vitamin. Doctors are still debating how much iodine is optimal, but the general recommended daily allowance is 150 mcg.