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Skin lesion KOH exam

Potassium hydroxide examination of skin lesion

The skin lesion KOH exam is a test to diagnose a fungal infection of the skin.

How the Test is Performed

Your health care provider scrapes the problem area of your skin using a needle or scalpel blade. The scrapings from the skin are placed on a microscope slide. Liquid containing the chemical potassium hydroxide (KOH) is added. The slide is then examined under the microscope. KOH helps dissolve much of the cellular material. This makes it easier to see if there is any fungus.

How to Prepare for the Test

There is no special preparation for the test.

How the Test will Feel

You may feel a scratching sensation when the provider scrapes your skin.

Why the Test is Performed

This test is done to diagnose a fungal infection of the skin.

Normal Results

No fungus is present.

What Abnormal Results Mean

Fungus is present. The fungus may be related to ringworm, athlete's foot, jock itch, or another fungal infection.

If the results are uncertain, a skin biopsy may need to be done.

Risks

There is a small risk of bleeding or infection from scraping the skin.

References

Babel DE. Fungal studies (and scabies): collection procedures and tests. In: Fowler GC, ed. Pfenninger and Fowler's Procedures for Primary Care. 4th ed. Philadelphia, PA: Elsevier; 2020:chap 17.

Elewski BE, Hughey LC, Hunt KM, Hay RJ. Fungal diseases. In: Bolognia JL, Schaffer JV, Cerroni L, eds. Dermatology. 5th ed. Philadelphia, PA: Elsevier; 2025:chap 77.

    • Tinea (ringworm)

      Tinea (ringworm) - illustration

      Ringworm is a common skin disorder, especially among children, but may occur in people of all ages. It is caused by mold-like fungi (dermatophytes).

      Tinea (ringworm)

      illustration

      • Tinea (ringworm)

        Tinea (ringworm) - illustration

        Ringworm is a common skin disorder, especially among children, but may occur in people of all ages. It is caused by mold-like fungi (dermatophytes).

        Tinea (ringworm)

        illustration

      Tests for Skin lesion KOH exam

       

      Review Date: 6/3/2025

      Reviewed By: Ramin Fathi, MD, FAAD, Director, Phoenix Surgical Dermatology Group, Phoenix, AZ. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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