Nummular Eczema: Understanding Those Coin-Shaped Itchy Patches

What Is Nummular Eczema?

Nummular eczema—also called nummular dermatitis or discoid eczema—is a type of eczema (skin inflammation) that produces distinctively round or oval patches on the skin. The word “nummular” comes from the Latin word for coin, which perfectly describes the shape of these lesions.

Unlike the diffuse, poorly bordered patches seen in other eczema types, nummular eczema creates well-defined circles that are hard to miss. The patches typically go through stages: starting as clusters of small red bumps and blisters, then becoming oozing and crusted, and finally drying into thick, scaly, leathery plaques if the condition becomes chronic.

Nummular eczema tends to flare during winter months when indoor heating dries out the air and skin. It is more common in adults aged 30–50 and shows a slight preference for men.

Signs and Symptoms

The most recognizable features of nummular eczema include:

• Coin-shaped patches measuring 1–3 centimeters (roughly the size of a dime to a quarter).
• Well-defined, clear borders that distinguish nummular eczema from other skin conditions.
• Patches start as red bumps and small blisters that merge into a disc-shaped area.
• The surface may ooze fluid and crust over before drying into scaly, thickened skin.
• The center of the patch sometimes clears, creating a ring-like appearance that can mimic ringworm.
• Intense itching, which is often worse at night and can disrupt sleep.
• Most common locations: lower legs and shins, tops of the feet and hands, forearms, and buttocks.

Secondary bacterial infection occurs in 30–40% of people during the course of nummular eczema, causing increased redness, swelling, pus, and sometimes fever. This is important to watch for and report to your doctor.

Causes and Risk Factors

The exact cause of nummular eczema is not fully known, but several factors contribute:

• Impaired skin barrier: The outer layer of skin in nummular eczema does not hold moisture as well as it should, leading to dryness and irritation. Measurements of transepidermal water loss (TEWL)—how much moisture escapes through the skin—are elevated in affected areas.
• Genetic factors: Mutations in the filaggrin gene (a protein that helps maintain the skin barrier) have been found in some patients. About 40% of people with nummular eczema have a personal or family history of atopic diseases like asthma, hay fever, or atopic dermatitis.
• Dry skin (xerosis): Very dry skin is a major trigger, especially in cold, low-humidity weather or when using harsh soaps.
• Contact allergens: Many patients develop sensitivity to topical products used during treatment, creating a secondary allergic contact dermatitis (skin allergy from touching certain substances).
• Bacteria: Staphylococcus aureus bacteria colonize (live on) the affected skin in 60–80% of cases and may worsen inflammation.
• Occupation: Healthcare workers, hairdressers, and people in wet-work jobs are at higher risk due to frequent skin contact with water and irritants.
• Emotional stress, wool clothing, and sweating are common personal triggers that patients identify.

How It’s Diagnosed

Nummular eczema is diagnosed primarily through a clinical exam—your doctor looks at the shape, size, location, and appearance of the patches. There is no single blood test that confirms it.

• Physical examination: The coin-shaped, well-bordered patches in typical locations are highly characteristic.
• Patch testing: If contact allergy is suspected (especially if certain products seem to trigger flares), patch testing applies small amounts of common allergens to the skin for 48 hours to identify sensitivities.
• KOH preparation or fungal culture: Since ringworm (tinea corporis) can look similar, a skin scraping may be examined to rule out a fungal infection.
• Skin biopsy: Rarely needed but can confirm the diagnosis by showing spongiosis (skin cell swelling), acanthosis (skin thickening), and a pattern of immune cell infiltration consistent with eczema.
• Bacterial culture: If the patches are oozing or crusted, a culture may be taken to check for secondary infection.

Treatment Options

Nummular eczema treatment focuses on rebuilding the skin barrier, reducing inflammation, and avoiding known triggers.

Skin care and moisturization:

• Apply thick moisturizers containing ceramides and hyaluronic acid immediately after bathing while the skin is still slightly damp. This is one of the most important steps.
• Use fragrance-free, gentle cleansers and avoid hot water, which strips natural oils.
• Wear soft fabrics (cotton) and avoid wool and synthetic materials against the skin.

Topical medications:

• Topical corticosteroids (steroid creams): The mainstay of treatment. Mid-to-high potency steroids (such as triamcinolone or fluocinolone) are applied once or twice daily to active patches for 2–4 weeks.
• Topical calcineurin inhibitors: Tacrolimus ointment or pimecrolimus cream are non-steroidal options used for sensitive areas like the face or when long-term steroid use is a concern.
• Topical antibiotics: If bacterial infection is present, mupirocin ointment or similar agents are added.

Oral medications for moderate-to-severe disease:

• Oral antibiotics (e.g., doxycycline or cephalexin) for documented bacterial superinfection.
• Short-course oral corticosteroids for rapid control of severe, widespread flares.
• Dupilumab (Dupixent): A biologic injection approved for moderate-to-severe eczema that targets specific immune pathways (IL-4 and IL-13) driving inflammation; particularly useful for patients who do not respond to standard therapy.

Phototherapy (light therapy): Narrowband UVB light therapy delivered 2–3 times weekly is effective for widespread or difficult-to-treat nummular eczema.

What to Expect / Recovery

• Nummular eczema tends to follow a chronic, relapsing course—it may clear with treatment but return, often in the same locations.
• With proper care, most patients can control flares effectively and reduce the frequency of recurrence.
• Itching may persist even after the visible patches have faded—this is normal and usually improves with continued moisturization.
• Skin darkening (post-inflammatory hyperpigmentation) or lightening may remain for months after patches resolve, especially in individuals with darker skin tones.
• Seasonal patterns are common: many patients flare in winter and improve in summer.
• Identifying and avoiding your personal triggers—whether stress, specific soaps, or dry air—is one of the best long-term management strategies.

When to See a Dermatologist

See a dermatologist if:

• You have round, itchy skin patches that have not responded to over-the-counter hydrocortisone cream within 2–3 weeks.
• Patches are spreading, becoming more numerous, or interfering with sleep or daily activities.
• The skin is oozing yellow crusts or becoming warm and swollen (signs of possible bacterial infection).
• You are unsure whether the rash is eczema or a fungal infection—they can look alike.
• Your current treatment is not working or you are using large amounts of steroid cream without improvement.

Frequently Asked Questions

Q: Is nummular eczema the same as ringworm?
A: No, though they can look similar. Ringworm is a fungal infection and responds to antifungal creams. Nummular eczema is an inflammatory skin condition caused by immune and barrier dysfunction, not a fungus. A dermatologist can tell them apart with a skin scraping test. Using antifungal cream on nummular eczema (or steroid cream on ringworm) will not help and may make things worse.

Q: Will nummular eczema ever go away completely?
A: For some people, it does resolve and never returns. For others, it is a recurring condition that flares periodically throughout life. The key is learning your triggers and maintaining good skin care habits to keep flares infrequent and mild.

Q: Is nummular eczema contagious?
A: No. Nummular eczema is not contagious—it cannot be spread from person to person. It is an inflammatory condition, not an infection (unless a secondary bacterial or fungal infection develops on top of the eczema).

Q: Can diet affect nummular eczema?
A: Diet is not a well-established trigger for nummular eczema specifically, unlike some other eczema types. However, staying well hydrated and maintaining overall health supports skin function. If you notice a consistent pattern between certain foods and flares, discuss this with your dermatologist.