At first glance, it can be tricky to tell nummular eczema (also called nummular dermatitis or discoid eczema) apart from ringworm. Both are skin conditions that cause round-shaped rashes that are red and itchy. Both involve rashes that often appear in clusters. And in both conditions, they can look like red rings surrounding otherwise unaffected skin.
Despite their similarities, there are key differences to help you distinguish nummular eczema from ringworm. Here, we will compare the two skin conditions, including what causes them and how they can be treated.
Despite their similar appearance, nummular eczema and ringworm (also called tinea corporis) are very different skin conditions. Nummular eczema is a chronic (long-lasting) condition caused by dry skin, other types of eczema, or trauma to the skin, such as a burn or injury. Nummular eczema is not contagious — it cannot be spread to others. Symptoms of nummular eczema may come and go throughout a person’s life. Patches of skin affected by nummular eczema can be red, scaly, and itchy.
Ringworm, on the other hand, is a contagious skin infection caused by fungi called dermatophytes. (There are no worms of any kind associated with ringworm.) A ringworm infection typically looks like a ring of red bumps and scaly skin surrounding clear, unaffected skin. It can also appear as patches of scaly red skin. If oral or topical antifungal medications are used to treat ringworm, it often clears up in two to four weeks.
The symptoms of nummular eczema and ringworm are similar. Both conditions cause red patches on the skin called plaques. Because of the round shape of plaques in each condition, it is easy to confuse nummular eczema and ringworm.
The plaques, although they look similar, have distinct differences that a primary care doctor or dermatologist can spot. In nummular eczema, plaques are usually like red, scaly, itchy coins. Nummular eczema plaques can occur in clusters, and are anywhere from 1 to 4 inches (2.5 to 10 centimeters) across. These plaques can also be dry or exudative (wet and oozy).
Ringworm, however, usually involves plaques that have a red, bumpy border with unaffected skin in the middle. It’s the borders in ringworm that are usually dry and scaly. Ringworm plaques also tend to occur one or two at a time, and may result in hair loss on the affected areas.
Ringworm and nummular eczema have different causes, which means a person could have ringworm and nummular eczema at the same time.
Ringworm is caused by fungi called dermatophytes. The condition is contagious and can be spread from person to person, animal (like a household pet) to person, and object to person (by touching a surface contaminated with the fungus). Very rarely, ringworm can also be spread through soil infected with dermatophytes.
Nummular eczema is not contagious, and there is no known single cause. This condition can affect anyone regardless of age. However, nummular eczema is slightly more common in women 15 to 25 years of age and older men in their 50s and 60s.
Certain triggers can contribute to the development of nummular eczema.
Like other forms of eczema, nummular dermatitis is often attributed to triggers like dry skin. Having particularly dry skin can weaken a person’s first physical barrier — the skin — against irritating substances and chemicals. As a result, coming into contact with otherwise harmless substances may cause skin irritation and itchiness. Using moisturizer daily can help alleviate dry skin and restore your skin barrier.
Contact dermatitis is a type of eczema that develops as a result of irritants or chemicals you may be allergic to coming into direct contact with your skin. Nummular dermatitis may be caused by allergic or irritant contact dermatitis and its triggers, such as nickel, mercury, and gold. If contact allergy is suspected, talk to your dermatologist about allergy testing called patch testing.
Some people with nummular dermatitis also have a history of atopic dermatitis (eczema). Atopic dermatitis is a chronic type of eczema that often develops in the first 6 months of a person’s life. Typically, atopic dermatitis appears as a dry, scaly, itchy rash that can be pink, red, purple, or dark brown depending on a person’s skin tone.
Some drugs can cause a person to develop drug-induced nummular dermatitis. This condition occurs when certain medications compromise the functioning of the skin’s outermost layer or the skin’s immune response.
Medications that can induce nummular dermatitis include:
In some cases, trauma to the skin — such as an injury, burn, or bug bite — may trigger a person to develop nummular dermatitis.
Nummular eczema and ringworm can both be diagnosed through a skin examination by your primary care provider or a dermatologist. Because the two conditions look similar, it is a good idea to have a doctor examine your skin rather than self-diagnose. Your heath care team can then determine what is causing your symptoms and prescribe the right treatment.
Other ways that doctors can diagnose nummular eczema or ringworm include swabbing or scraping your rash for a cellular sample that can then be microscopically evaluated.
Skin swabs involve brushing a long cotton swab over the affected area. The swab is then examined under a microscope for signs of eczema or for dermatophytes. Dermatophytes may indicate a ringworm infection.
In a skin scraping procedure, your doctor gently removes flakes of skin from the rash with a small razor. The doctor then checks the flakes of skin under a microscope. This procedure is similar to shaving your body to remove body hair and does not hurt.
Fungal cultures involve brushing a long cotton swab over your rash and sending the swab to a lab to check for ringworm.
Nummular eczema and ringworm require different approaches to treatment. With nummular eczema, treatment focuses on both preventing symptoms from occurring and treating flare-ups when symptoms reoccur. Nummular eczema is a chronic condition that may come and go throughout a person’s life. Ringworm, on the other hand, can be treated with medications and usually clears up in 2 to 4 weeks.
Treating nummular eczema often begins with prevention methods. Common ways of preventing nummular eczema include:
When you experience a flare-up from nummular eczema, common treatments include medication and phototherapy.
Prescription or over-the-counter (OTC) medications to treat nummular eczema can include oral or topical corticosteroid medications, which lessen inflammation throughout the body. (While steroid creams are most commonly used, steroid-free options like crisaborole, pimecrolimus, and tacrolimus are sometimes substituted.)
Treatment may also include antihistamines, which help treat allergy symptoms and alleviate itching. Antibiotics may also be used, especially if the eczema plaques become infected.
Phototherapy (light therapy) is a type of therapy that uses a machine to create ultraviolet A (UVA) or ultraviolet B (UVB) rays. These rays are light similar to sunlight. With phototherapy, the machine is used on your skin throughout multiple sessions for seconds or minutes over a series of sessions.
The most common treatments for ringworm are antifungal creams, ointments, shampoos, or pills. Topical creams containing clotrimazole, miconazole, and terbinafine are commonly used. If a person’s ringworm rash is extensive, oral antifungals (such as fluconazole or terbinafine) can also be used as a treatment.
During treatment for ringworm, it is important to prevent spreading ringworm to others. You can prevent ringworm from spreading with the following tips:
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Have you ever experienced nummular eczema and/or ringworm? Did you have trouble telling the two conditions apart? Share your experience in the comments below or by posting on MyEczemaTeam.