How Ringworm Is Diagnosed

The most common way to diagnose ringworm is by a simple visual inspection of the rash. Ringworm generally forms a very distinctive ring-shaped rash that is easy to identify once you've seen it (although the rash does look different depending on where it's found on the body). If necessary, testing can be performed to confirm the presence of the fungi (dermatophytes) that cause ringworm.

Self-Checks/At-Home Testing

If you have an itchy, raised, ring-shaped rash that slowly grows outward as it spreads, suspect ringworm.

Also, look for clues. Ringworm can be transmitted from infected animals (cats, dogs, or livestock) to people. Cats are especially susceptible. Patchy hair loss or areas of crusty skin are signs that your pet has ringworm. If you have contact with these animals, you may have contracted ringworm even if you don't notice symptoms yourself.

Often, though, you won't know where you could have picked up ringworm.

Labs and Tests

Your healthcare provider can usually diagnose ringworm with a simple visual inspection of the skin.

When ringworm appears on the body, legs, and arms, it creates the classic raised, red ring-shaped rash which makes diagnosis fairly simple. However, if ringworm appears on other areas of the body, diagnosis can become tricky—sometimes, ringworm might show up as bumpy, scaly, flaky patches that resemble other skin problems.

Ringworm Doctor Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

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KOH Test

If there's any uncertainty, your healthcare provider will do a KOH test. This simple test, sometimes just called a skin scraping, can be done in your healthcare provider's office. Your healthcare provider will use a scalpel or the edge of a glass slide to scrape a small bit of infected skin. The scrapings will be collected onto a microscope slide or into a test tube.

If suspected ringworm is infecting your scalp or beard area, your healthcare provider might also take some hair to examine. For affected nails, the healthcare provider will take a small clipping of nail and a scraping from underneath the nail as well.

The samples are prepared with potassium hydroxide (KOH) solution and viewed under a microscope to look for the fungi that cause ringworm infections. If dermatophytes are found, your healthcare provider knows conclusively that ringworm is the culprit.

If no fungus is found, something other than ringworm is causing your rash.

Fungal Culture

If the results of the KOH test are inconclusive, meaning they don't give an answer one way or another, your healthcare provider may do a fungal culture. A skin scraping is done as before, but this time it will be sent to a lab where it will be incubated. Any fungi present in the sample will grow.

The downside is that it can take several weeks to get results from this test. The upside is that with the results, you can know the specific strain of fungi that is causing your rash.

Differential Diagnoses

Ringworm can be mistaken for other skin problems, especially when it develops on areas other than the arms, legs, and trunk.

Ringworm on the body can resemble:

• Eczema, especially nummular eczema (a type of dermatitis that causes round, raised, red patches)
• Pityriasis rosea
• Psoriasis
• Lyme disease (this disease is much less common than ringworm)

Ringworm of the scalp or beard area can resemble:

• Folliculitis (especially in the beard area)
• Alopecia areata
• Seborrheic dermatitis