The skin lesion KOH exam is a simple test that helps doctors identify fungal infections on a persons skin, hair, and nails. When doctors perform a KOH exam, they take a skin scraping, which they then place in a potassium hydroxide (KOH) solution and analyze under a microscope. The potassium hydroxide destroys the healthy skin cells, leaving behind only fungal cells. Normal results of a KOH test will show no fungi present, while abnormal results will tell your doctor that you may have a fungal infection.