From Heather Brannon, MD,
Your Guide to Skin & Beauty.
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About.com Health's Disease and Condition content is reviewed by Casey Gallagher, MD

Definition: A KOH test is used to diagnose fungal infections of the skin or nails. The skin or nail is scraped with a scalpel or glass slide causing dead skin cells to fall off onto a glass slide. A few drops of Potassium hydroxide (KOH) are added to the slide and the slide is heated for a short time. The KOH dissolves the material binding the skin cells together releasing the fungus. The slide is then viewed under the microscope looking for fungal elements.