The most common way to diagnoseringwormis by a simple visual inspection of the rash.
Also, look for clues.
Ringworm can be transmitted from infected animals (cats, dogs, or livestock) to people.
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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 noticesymptomsyourself.
Often, though, you won’t know where you could have picked up ringworm.
Get our printable guide for your next healthcare provider’s appointment to help you ask the right questions.
Other skin rashes can resemble ringworm, and it can sometimes be hard to tell the difference.
Treating ringworm or any rash incorrectly can make the rash worse.
Get our printable guide for your next healthcare provider’s appointment to help you ask the right questions.
KOH Test
If there’s any uncertainty, your healthcare provider will order aKOH test.
The scrapings will be collected onto a microscope slide or into a test tube.
Your healthcare provider only needs skin cells for the test; you won’t be cut.
The scraping itself may be mildly uncomfortable but it’s not painful.
If suspected ringworm is infectingyour scalpor beard area, your healthcare provider might also take some hair to examine.
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.
Any fungi present in the sample will grow.
The downside is that it can take several weeks to get results from this test.
Some infections may be tenacious and tough to treat.
Knowing this can help your healthcare provider find the most effective medicine for you.
A fungal culture is performed by putting skin scrapings in a sterile culture medium.
A Woods lamp has limited usefulness in diagnosing ringworm because a negative finding does not rule out the infection.
Cornell University College of Veterinary Medicine.Ringworm: a serious but readily treatable affliction.
Centers for Disease Control and Prevention.Clinical overview of ringworm and fungal nail infections.
Bosshard PP.Incubation of fungal cultures: how long is long enough?Mycoses.
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Al Aboud DM, Gossman W.Woods light.
StatPearls Publishing; 2025.
