Lugol's iodine (aqueous iodine) is a solution of potassium iodi*de and iodine in water, used primarily as an antiseptic, disinfectant, and diagnostic tool in medical settings. It stains glycogen in normal cells brown, helping identify can*cer cells (which remain unstained) in the esophagus or cervix. It is also used in emergencies to prevent radioactive iodine uptake in the thyroid.