Skin Scraping - What It Is & How Does It Work

What Is a Skin Scraping?

In dermatology, a potassium hydroxide (KOH) skin scraping is a common procedure used to obtain the superficial dead layers of the skin. This procedure is most often used to diagnose fungal skin infections, such as athlete's foot or tinea infections of the body. In some cases, a mineral oil scraping, instead of a KOH skin scraping, is used to diagnose parasitic skin infections such as scabies. 

How Does a Skin Scraping Work?

The KOH or mineral oil based skin scraping allows the dermatologist to obtain a sample of skin in order to check for parasites or fungus under the microscope. It is a quick, simple, and relatively inexpensive test that allows the dermatologist to look for certain infections. Potassium hydroxide (KOH) is often applied to the specimen on the microscope slide, which dissolves skin cells (keratinocytes), mucus, and other debris, and makes the organisms easier to see.^[1] Mineral oil is often applied to immobilize any parasites like scabies so that they are more easily seen under the microscope. 

What Conditions Are Skin Scrapings Used For?  

Skin scrapings are used to diagnose several conditions including:  

1. Fungal Infections

Tinea pedis (athlete's foot: fungal infection of the feet) 

Tinea corporis (fungal infections of the body)

2. Yeast Infections

Candida 

Tinea versicolor (caused by the yeast Malassezia furfur)

3. Parasitic Infections

Scabies

Lice

How Are Skin Scrapings Done?

If a dermatologist suspects a parasitic or fungal infection of the skin, they may choose to use skin scrapings of affected sites in order to obtain a sample of tissue. 

• Selecting where to scrape: skin scrapes are usually done in areas with visual signs of infestation.
• Depending on the sample site, a small window of hair may first have to be shaved away. If the infection is suspected under the fingernails or toenails, the nails will first be trimmed back. After which, the area will be sterilized with alcohol.
• Mineral oil may be first applied to the skin to help with ease of scraping and collection, especially if looking for scabies.
• The dermatologist will use a scalpel blade to scrape perpendicularly across the skin, often in a 1-2 inch area. In the case of oral infection, a tongue blade may be used to scrape a specimen onto a slide.
• To prepare the glass slide, a few drops of KOH will be added to the skin sample, and then a coverslip will be placed over the top.
• The dermatologist will then view the slide starting at low light and magnification. If hyphae or pseudohyphae are visualized, there is a strong likelihood of a dermatophyte (fungal) or yeast infection, respectfully.
• If the KOH preparation turns out negative, there may still be a need for a fungal or yeast culture to confirm the diagnosis.

What Are Common Risks and Potential Side Effects for Skin Scraping?

There is a risk for bleeding at the scraped site.