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Home > Wellness Resources > Health Library > KOH (Potassium Hydroxide) Preparation
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.
A doctor may do a KOH test to find out whether a person
has a fungal infection. Fungal infections may cause:
Findings of a KOH test may include the following:
No fungi are present in the nail, skin, or hair samples.
Other tests may be done to find out the cause of the skin
Fungi are present in the nail, skin, or hair samples.
Your doctor may be able to find out whether you have a fungal
infection by the appearance of the rash and may not need to do a KOH
Complete the medical test information form (PDF)medical test information form (PDF)(What is a PDF document?) to help you prepare for this test.
Current as of:
March 12, 2014
Kathleen Romito, MD - Family Medicine & John Pope, MD - Pediatrics
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