How to Tell the Difference Between Nummular Eczema and Ringworm

Nummular eczema and ringworm look very similar, which makes it very difficult for the average person to distinguish it. “Even a general doctor without an expertise in dermatology can have a hard time spotting the subtle differences between ringworm and nummular eczema,” said dermatologist Dr. Benjamin Ungar, director of the Alopecia Center of Excellence and director of the Rosacea & Seborrheic Dermatitis Clinic at Mount Sinai in New York. 

“The differences in appearance can often be subtle,” Dr. Ungar said. Plus, the treatments for each skin condition are different. Dr. Ungar suggests seeing a dermatologist so you can get a correct diagnosis.

What is nummular eczema and how is it treated?

Nummular eczema, also known as discoid eczema and nummular dermatitis, is an inflammatory condition that appears as scattered circular patches on the skin. The circular patches are often itchy and oozing. The word “nummular” comes from the Latin word for “coin,” as the spots can look coin-shaped on the skin. 

“Nummular eczema is usually treated with an anti-inflammatory treatment, often something like a topical steroid,” said Dr. Ungar. 

What is ringworm and how is it treated?

“Ringworm is a bit of a misnomer because it is, in fact, caused by a fungus”, Dr. Ungar said. Ringworm is not caused by a worm.  

Ringworm is a superficial fungal infection, typically treated with a topical antifungal cream. Occasionally, ringworm may need to be treated with an oral or systemic antifungal medicine.

How do dermatologists diagnose nummular eczema vs. ringworm? 

Since nummular eczema and ringworm look so alike on the skin, there aren’t any hard and fast rules to distinguish the two, said Dr. Ungar. 

“There’s not one approach to diagnose ringworm and nummular eczema,” Dr. Ungar said. There are often clinical clues that may be more subtle that a dermatologist with training and experience can identify.

“One clue that can sometimes be used to distinguish between the two is that ringworm will often have some clearing or more normal-appearing skin in the center of the lesion with more of the scaling and red part of it towards the periphery,” Dr. Ungar said. But, he added, nummular eczema can sometimes look like this as well, so it’s not an ironclad rule. 

Nummular eczema also tends to affect the limbs, like arms and legs, more than the trunk of the body, like the chest and back. In contrast, ringworm can appear anywhere on the body. 

People can also get a fungal infection in areas, like the groin. “This is typically referred to as jock itch rather than ringworm,” said Dr. Ungar. This is still considered a superficial fungal infection, it just appears a little different depending on the part of the body it is showing up on.

In some rare cases, a biopsy or scraping can help with diagnosis.

When should you see a doctor?

If you see circular patches on your skin, and you’re not sure what they are, you should go see a dermatologist so they can diagnose it.

“I don’t really encourage people to try to self-diagnose because the treatment approaches are different,” Dr. Ungar said. These skin conditions can easily be confused. Your best option is to see a dermatologist. Let the experts figure it out.