Nummular eczema: the coin-shaped rash

What it is

“Nummular” means coin-shaped. This eczema pattern develops when the skin barrier becomes dry and inflamed. It can occur at any age, often after an injury, insect bite, harsh weather or a period of very dry skin.

Unlike an infection, eczema is not contagious. However, scratching can damage the barrier and lead to secondary bacterial infection. Treatment aims to restore moisture, calm inflammation and identify aggravating exposures.

What it looks and feels like

• Round or oval patches ranging from small spots to several centimeters.
• Intense itch, burning or tenderness.
• Early lesions may contain tiny blisters, ooze or form crust.
• Older patches become dry, scaly, thickened or darker/lighter than surrounding skin.
• Often affects arms and legs; multiple lesions may appear at once.

Causes, triggers and risk factors

• Very dry skin, low humidity and cold weather.
• Hot showers, harsh soap, fragrance and frequent cleansing.
• Minor injury, scratching, insect bite or chemical irritation.
• Contact allergy to metals, topical products or medications in some cases.
• Stress and poor sleep can intensify itch and scratching.

Treatment and self-care

Use short lukewarm showers and a fragrance-free gentle cleanser only where needed. Within minutes of bathing, apply a thick cream or ointment rather than a thin lotion. Reapply at least twice daily and protect skin from friction and cold dry air.

A clinician may prescribe a topical corticosteroid or another anti-inflammatory medicine. Wet wraps or phototherapy may be considered for widespread disease. Do not apply steroid alone to a possible fungal infection without advice, because it can mask ringworm.

Conditions that can look similar

• Ringworm: often has an advancing scaly edge and partial central clearing.
• Contact dermatitis: distribution corresponds to an exposure.
• Psoriasis: usually thicker plaques with characteristic sites or nail changes.
• Stasis dermatitis: lower-leg inflammation associated with swelling and vein disease.
• Skin infection: rapidly worsening pain, warmth, pus or honey-colored crust needs review.

Nummular eczema vs. ringworm

Both can be circular and scaly. Ringworm more often grows outward with a raised active edge while the center becomes less inflamed. Nummular eczema may be uniformly inflamed, very itchy and accompanied by dry skin elsewhere. These clues are imperfect—clinicians can scrape the edge and examine it for fungus.

If you are unsure, avoid mixing antifungal and steroid products randomly. A targeted diagnosis prevents weeks of treating the wrong condition.

When to see a healthcare professional

• The diagnosis is uncertain and ringworm is possible.
• Patches are rapidly spreading, painful, warm, draining or crusted.
• Sleep is repeatedly disrupted or large areas are involved.
• Correct skin care and prescribed treatment do not improve the eruption.
• The rash repeatedly returns in the same place or follows a particular product.

Sources and further reading

We use established public-health and dermatology references and link them directly so you can verify the guidance and read further.

• Nummular eczema diagnosis and treatment — American Academy of Dermatology
• Eczema — U.S. National Library of Medicine

More free skin tools from RashScan