Lugol’s solution is an aqueous solution of iodine and potassium iodide. Lugol’s solution is used in cytology for detecting abnormal squamous cells of the vaginal epithelium and cervix epithelium by using the Schiller’s test (used during colposcopy)

Lugol’s solution stains normal epithelium dark brown, useful for delineating abnormal epithelium, for defining the borders of a lesion.