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Skin scraping

A small scrape of the affected skin, examined under a microscope with KOH — the quick test for a fungal infection.

Updated: August 29, 2026·MedProtect editorial team
Reference information — not a diagnosis or a prescription
In shortThe provider scrapes the problem area of skin with a needle or scalpel blade. The scrapings go onto a microscope slide, potassium hydroxide (KOH) is added to dissolve the cellular material, and the slide is examined for fungus. No special preparation is needed.

A skin scraping answers a narrow question well: is a fungus living in this patch of skin? The test is the skin lesion KOH exam, named after potassium hydroxide, the chemical that makes the answer visible.

The procedure is simple. The provider scrapes the problem area of the skin using a needle or a scalpel blade. The scrapings are placed on a microscope slide, and liquid containing KOH is added. KOH dissolves much of the cellular material — skin cells break down, fungal cells survive — so under the microscope it becomes much easier to see whether any fungus is present.

There is no special preparation for the test. What is felt during it is a scratching sensation as the skin is scraped. Afterwards there is a small risk of bleeding or infection at the scraped spot — the same minimal risk as with any superficial scratch.

The result is read as a yes-or-no answer: no fungus present, or fungus seen. A negative result does not always close the question — too few fungal cells in the sample, imperfect collection, slow-growing organisms, a sample stored or delivered badly, or antifungal creams used at home before the visit can all hide a fungus that is actually there. When suspicion stays high, the provider can repeat the scraping or add other tests.

How the sample is collected

  1. No preparation is needed — arrive with the skin as it is.
  2. Mention any antifungal creams or ointments already used on the area; they can hide the fungus from the microscope.
  3. The provider scrapes the problem area with a needle or scalpel blade — a scratching sensation, seconds long.
  4. The scrapings go onto a slide with KOH and are examined under a microscope.
  5. Watch the scraped spot afterwards; prolonged bleeding or signs of infection are a reason to tell the provider.

What can spoil the sample

  • Applying antifungal cream before the visit — the test can come back falsely negative.
  • Scraping or washing the area aggressively right before the appointment.
  • Treating a negative result as final when symptoms persist — a repeat scraping or another test may still find the cause.

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Frequently asked questions

Why is KOH added to the sample?
Potassium hydroxide dissolves most of the ordinary cellular material on the slide while fungal cells survive, so the microscope shows the fungus clearly instead of hiding it among skin cells.
Does the scraping hurt?
It feels like a scratching sensation while the provider works — brief and superficial. There is a small risk of bleeding or infection, as with any scratch.
Can the test miss a fungus?
Yes. Too few fungal cells in the sample, slow-growing organisms, poor storage or delayed delivery, and antifungal products used at home beforehand can all produce a false negative. Persistent symptoms after a negative result are a reason to retest.

Sources

  1. Skin lesion KOH exam: MedlinePlus Medical Encyclopedia — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.