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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.

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:

Results

Findings of a KOH test may include the following:

Normal

No fungi are present in the nail, skin, or hair samples.

Other tests may be done to find out the cause of the skin infection.

Abnormal

Fungi are present in the nail, skin, or hair samples.

What To Think About

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 test.

Complete the medical test information form (PDF)(What is a PDF document?) to help you prepare for this test.

By Healthwise Staff
Primary Medical Reviewer Kathleen Romito, MD - Family Medicine
Specialist Medical Reviewer John Pope, MD - Pediatrics
Current as of March 12, 2014

WebMD Medical Reference from Healthwise

Last Updated: March 12, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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