A potassium hydroxide (KOH) test is done to determine whether a
fungus is causing a skin infection. Samples from an infected area are treated
with KOH, which dissolves skin cells and leaves behind fungus cells (if any are
present) that can been seen with a microscope.
The KOH test may be used to diagnose fungal infections, such as
thrush, tinea versicolor, and ringworm.