The doctor or nurse places the nail, skin or hair sample on a
slide with potassium hydroxide (KOH) solution and gently heats
it. This solution slowly dissolves the skin cells but not the
fungus cells. The fungus cells are then visible with a
microscope. Color stains may be used so that the fungus is
easier to see. Why It Is Done A doctor may do a KOH test to
determine whether a person has a fungal infection. Fungal
infections may cause: Ringworm of the scalp or beard. With this
infection, a person has flakes of dead skin (dandruff) on the
hair; broken, crusted, or matted hair; redness or irritation of
the scalp or beard; swollen areas and blisterlike bumps with pus
(kerions); and/or hair loss. Ringworm of the skin. With this
infection, a person has patches of skin that are itchy, red, or
scaly, with blisterlike bumps on the edges. Athlete's foot. With
this infection, a person has peeling, cracking, and scaling on
the bottoms of their feet or between the toes, or blistered skin
on their feet. Findings of a KOH