Potassium Hydroxide (KOH) preparation for hair is a rapid microscopic test specifically designed to detect hair fungi (dermatophytes). Samples of affected hair (with roots if possible) or scales from the scalp are taken, placed on a microscope slide with KOH solution (10-20%). The solution dissolves the keratin material in the hair shaft, making the fungal spores (arthroconidia) inside or on the hair surface visible under the microscope.