Nummular Eczema (ICD-10: L30) ⚠️

Nummular Eczema: Coin-Shaped Patches of Inflamed Skin

Nummular eczema, also called discoid eczema, produces round or oval patches of inflamed skin with unusually sharp edges. The name comes from the Latin nummus, a coin, and the shape is its most recognisable feature: a well-defined disc, typically one to several centimetres across, sitting on otherwise normal-looking skin.

The patches are intensely itchy. Early on they are studded with tiny vesicles and may weep; later they dry, scale and crust. They appear most often on the lower legs, the backs of the hands and forearms and the trunk, and they are frequently multiple and roughly symmetrical.

Incidence has two peaks: young adults, and again between the fifties and the seventies. Men are affected slightly more often in the older group. The condition is notably stubborn — individual patches can persist for months and tend to recur in the same places.

Predisposing Factors: Why Nummular Eczema Develops

The mechanism is not fully established. What is clear is that a damaged skin barrier is central, and that most of the recognised triggers act by drying or irritating the skin.

• Dry skin: The association reported most consistently, though the condition is multifactorial and no single cause has been established. Episodes cluster in winter, in centrally heated homes and in people who wash frequently in hot water.
• Age-related skin changes: Reduced barrier lipids in older skin explain the second incidence peak.
• Atopy: Present in a proportion of patients, particularly those who develop the condition young, but many people with nummular eczema have no atopic history at all.
• Local trauma: Patches sometimes begin at the site of an insect bite, a scratch, a burn or a previous area of inflammation.
• Contact allergy: Identified in a proportion of patients whose disease resists treatment. Patch testing is worthwhile in that group rather than routinely.
• Alcohol and certain medications: Heavy alcohol use is associated with more extensive disease, and some drugs — including interferon and certain targeted therapies — can provoke it.
• Venous disease: Patches on the lower legs may accompany venous insufficiency, which changes how they should be managed.

Diagnostics: How Nummular Eczema Is Diagnosed

Diagnosis is clinical, based on the shape, the sharp margin, the itch and the distribution. The important work at this stage is exclusion rather than confirmation, because several other conditions produce round patches and each needs different treatment.

Direct microscopy of scrapings is used to rule out ringworm, which can be almost indistinguishable to the eye. This matters practically: applying a corticosteroid to a fungal infection suppresses the inflammation while the infection spreads, producing an altered and harder-to-diagnose picture.

Patch testing is indicated when the disease is persistent, widespread or keeps returning despite good treatment. Biopsy is reserved for a solitary patch that does not respond, where an early skin cancer such as Bowen’s disease, or a cutaneous lymphoma, has to be excluded. A bacterial swab is taken when a patch is weeping, crusted and painful.

Symptoms: What Nummular Eczema Looks Like

• Coin-shaped plaques: Round or oval, with a distinctly sharper border than most forms of eczema, usually 1–5 cm across.
• Vesicles and weeping early on: Tiny blisters across the surface of a fresh patch, which ooze and then crust.
• Scaling and dryness later: As the patch matures it becomes dry, scaly and sometimes thickened from scratching.
• Intense itch: Frequently worse at night and often the symptom that brings people to a clinician.
• Clearing in the centre: Some patches fade centrally, which adds to the resemblance to ringworm.
• Post-inflammatory colour change: Patches commonly leave darker or lighter marks after the inflammation settles, particularly in deeper skin tones. These fade slowly and are not scars.

Differential Diagnosis: Ruling Out Other Conditions

• Tinea corporis (ringworm): Usually has a more active, scaly leading edge with central clearing; microscopy distinguishes them.
• Plaque psoriasis: Thicker, silvery scale, favours elbows, knees and scalp, and is typically less itchy.
• Bowen’s disease: A single persistent scaly patch, often on sun-exposed skin, that does not respond to steroid treatment. A solitary patch that stays unchanged after proper treatment should be reassessed rather than treated again, and biopsied if it remains atypical or uncertain.
• Mycosis fungoides: A cutaneous lymphoma that can mimic eczema for years; persistence and an atypical distribution raise the question.
• Allergic contact dermatitis: Shape follows the exposure rather than forming discs.
• Impetigo: Golden crusting spreading rapidly, usually in children.

Risks: Why Nummular Eczema Should Be Treated

Nummular eczema does not threaten health directly, but it is one of the more persistent forms of eczema and the consequences of leaving it accumulate. Scratching thickens the skin, which makes the itch harder to control and the patch slower to clear — a cycle that is easier to interrupt early than late.

Broken and weeping skin is readily colonised by bacteria, and secondary infection is common enough that it should be looked for whenever a patch becomes painful, golden-crusted or rapidly worse. Sleep disruption from night-time itch is a genuine burden, and prolonged inflammation frequently leaves pigment changes that take months to fade.

Tactics: When and How to Seek Treatment

See a clinician if round itchy patches appear and do not settle with a moisturiser within a couple of weeks, if they weep or crust, if they keep returning in the same places, or if a single patch persists unchanged despite treatment. That last point is worth emphasising: a solitary scaly patch that resists treatment is the presentation where another diagnosis needs excluding.

Over-the-counter antifungal creams are often tried first because of the resemblance to ringworm. If a patch has not improved on an antifungal within two weeks, the answer is a clinical reassessment rather than another course. Where ringworm still looks plausible, testing settles it; combined steroid and antifungal creams applied without a diagnosis tend to muddle the picture further.

Treatment: Modern Strategies for Nummular Eczema

• Emollients, generously and often: The foundation of treatment, not an optional extra. Ointments are more effective than lotions on dry, scaly plaques, and a soap substitute should replace ordinary soap.
• Topical corticosteroids: Nummular patches generally need a stronger preparation and a longer course than other eczemas, chosen by site and severity. Undertreatment is a frequent reason for apparent failure, but so are an unrecognised fungal infection, contact allergy, venous disease and an incorrect diagnosis — so a patch that is not responding should be reassessed rather than simply treated harder.
• Wet wrap dressings: Used over topical treatment on stubborn patches to increase absorption and stop scratching.
• Treatment of secondary infection: Topical or oral antibiotics where there is genuine bacterial infection, guided by a swab, rather than routinely.
• Topical calcineurin inhibitors: An option for maintenance or for sites where repeated potent steroid use is unsuitable.
• Phototherapy: Narrowband ultraviolet B is effective for widespread or recurrent disease.
• Systemic therapy: Considered by a dermatologist for severe, extensive or refractory disease.
• Managing the underlying problem: Where patches sit on the lower legs with venous insufficiency, addressing the venous disease changes the outcome more than topical treatment alone.

Prevention: Reducing Recurrence

• Keep the skin barrier intact: Moisturise daily, all year, and increase it in winter.
• Short, lukewarm showers rather than long hot baths, and a soap substitute instead of soap.
• Consider humidifying centrally heated rooms during the heating season; the evidence for it is limited, and too much humidity encourages mould.
• Avoid wool and rough fabrics directly against affected skin.
• Keep nails short to limit the damage from scratching, and treat the itch rather than enduring it.
• Reduce alcohol where intake is high, since it is associated with more extensive disease.
• Act on early patches instead of waiting; a fresh patch responds far faster than a thickened one.

Nummular eczema is slow to clear and inclined to return, which makes consistent barrier care between episodes as important as the treatment of an active patch. Most people achieve good control, but it takes persistence on both sides.