KOH Preparation for Fungal Elements

KOH (potassium hydroxide) preparation is a simple lab test for skin, nail or hair scrapings to detect fungal elements. A drop of 10–20% KOH is added to the specimen to dissolve keratin, clearing background material so hyphae or spores become visible on light microscopy. It’s rapid and inexpensive but not fully sensitive; negative tests may need culture or biopsy for confirmation.

Collect skin scrapings from the active lesion edge with a sterile scalpel, placing them on a glass slide. Add a drop of 10–20% KOH (use 20–40% for nails/hair), apply a coverslip, and warm gently or wait 10–30 minutes until tissue clears. Examine under a light microscope (10×/40×) for hyphae/arthroconidia. Wear gloves and eye protection; avoid KOH contact with skin.

Collect a small skin scraping, nail clipping, or hair root and place on a glass slide. Add one drop of 10–20% KOH for skin/hair (20–40% for thick nails), apply a coverslip, and gently press. Warm briefly or incubate 10–30 minutes to clear keratin. Examine under low then high power microscopy. Wear gloves, eye protection, and dispose of KOH-contaminated materials safely.

The two commonly recommended potassium hydroxide concentrations for mycological microscopy are 10% and 20% KOH. Typically, 10% KOH is used to clear skin and hair specimens, while 20% KOH is applied for thicker specimens such as nail clippings (often with gentle heating or DMSO to speed clearing). These concentrations provide effective clearing without excessive keratin digestion.

Potassium hydroxide (KOH) is used on skin or nail scrapings to dissolve keratin and other cellular debris. Its strong alkaline action digests epidermal cells and clears background material so fungal hyphae and spores—relatively resistant protein–chitin structures—stand out under the microscope. A KOH preparation doesn’t identify species but makes fungi visible for diagnostic examination.

To prepare 1 M KOH: weigh 56.11 g solid KOH per liter. In a suitable beaker, add the KOH slowly to about 800 mL deionized water while stirring (do not pour water into KOH); the mix will get hot. After dissolution and cooling, transfer to a 1 L volumetric flask and dilute to the mark. Wear gloves, goggles, and work in a fume hood; label and store safely.