The KOH test (potassium hydroxide preparation) is a diagnostic procedure used to detect fungal infections on the skin, hair, or nails. A sample from the affected area is placed on a microscope slide, treated with a potassium hydroxide solution, and examined under a microscope. The KOH dissolves skin cells and other debris, making fungal elements like hyphae or spores easier to see. This test is commonly used to diagnose conditions such as ringworm, candidiasis, and athlete’s foot, and provides a quick and cost-effective way to confirm fungal involvement.