Doctors use the KOH preparation to find out whether a fungal
infection is present on the nails, skin, scalp, or beard.
A doctor or nurse takes a sample of skin by lightly scraping the
infected area that is scaling or flaking.
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 find out 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.
How this information was developed to help you make better health decisions.