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

Potassium hydroxide examination of skin lesion

The health care provider scrapes the lesion off your skin, using a blunt edge such as the edge of a microscope slide. The scrapings from the skin lesion are placed in liquid containing potassium hydroxide (KOH) and examined under the microscope. KOH destroys all non-fungal cells, which makes it easier to see if there is any fungus present.

There is no special preparation for the test.

You may feel pressure when the doctor scrapes the lesion off your skin.

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

Normally, there is no fungus.

The KOH smear shows fungus, which may be related to ringworm, athlete's foot, jock itch, or another fungal infection.

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