Nummular Dermatitis

Nummular dermatitis: This skin problem often causes coin-shaped rashes on the skin that can itch or burn.

Nummular dermatitis: Overview

Also called discoid eczema

People who get this skin problem often see distinct, coin-shaped (nummular) or oval sores on their skin. Nummular dermatitis often appears after a skin injury, such as a burn, abrasion (from friction), or insect bite. A person may see 1 or many patches. These patches can last for weeks or months.

Your dermatologist may refer to this skin condition as:

• Nummular dermatitis.
• Nummular eczema.
• Discoid eczema.

Men get nummular dermatitis more often than women get it. Men often have their first outbreak between 55 and 65 years of age. When women get it, they are usually younger. They tend to be teenagers or young adults.

Image used with permission of the American Academy of Dermatology National Library of Dermatologic Teaching Slides.

Nummular dermatitis: A patch of nummular dermatitis on a patient's ankle.

Nummular dermatitis: Signs and symptoms

Patches on the skin tend to begin as a group of tiny, reddish spots and blister-like sores that weep fluid. Then the sores enlarge and grow together to form a coin-shaped patch.

The patches tend to have these signs and symptoms:

• Range in size from smaller than 1 inch to bigger than 4 inches.
• Occur most often on the legs but also occur on the torso (middle of the body), arms, hands, and feet.
• Be pink, red, or brown and well-defined.
• Itch and burn: These symptoms range from very mild to severe. The itch may be worse at night, disturbing sleep.
• Become crusty after the blisters leak fluid and, after a long time, become scaly.

A yellowish crust may develop on the patches if a Staphylococcus aureus (staph) infection occurs. This may require treatment with an antibiotic.

The skin between the patches often remains clear, but it can be dry and easily irritated.

Images used with permission of the American Academy of Dermatology National Library of Dermatologic Teaching Slides.

Nummular dermatitis: Blisters can form and grow together to create red patches.

Nummular dermatitis: Who gets and causes

Who gets nummular dermatitis?

This skin problem is more common in men than in women. Men tend to have their first outbreak between 55 and 65 years of age. Women are more likely to get it between the ages of 15 and 25 years. It is rare in children.

What causes nummular dermatitis?

While the cause is unknown, researchers think that sensitivity plays a role in some cases. A person may be sensitive to:

• Metals, including nickel and rarely mercury, such as from dental fillings.
• Formaldehyde.
• Medicines, such as neomycin (an antibiotic that you apply to the skin).

If the person has a sensitivity to something, the skin will only clear when the person avoids that substance.

Research also suggests that your risk of getting nummular dermatitis increases if you live in a cold, dry climate or have:

• Very dry skin (xerosis).
• Another type of eczema, mainly atopic dermatitis or stasis dermatitis.
• Poor blood flow and/or swelling in the legs.
• Injured your skin (insect bite, contact with chemicals, or abrasion).
• A skin infection caused by bacteria.
• Taken certain medicines, such as isotretinoin and interferon. Isotretinoin, a prescription medicine sometimes used to treat severe acne, seems to increase the risk for this skin problem. Interferon can cause severe widespread nummular dermatitis.

Nummular dermatitis: Diagnosis and treatment

How do dermatologists diagnose nummular dermatitis?

Dermatologists often diagnose nummular dermatitis by looking at the patient’s skin. During the exam, the dermatologist may swab the sores if the doctor thinks you have a skin infection.

If your dermatologist thinks you have an allergy, patch testing (skin tests to find allergies) may be recommended. Your dermatologist also may recommend patch testing if treatment does not fully clear your skin. An allergy can prevent the skin from clearing.

How do dermatologists treat nummular dermatitis?

These sores can be stubborn, so seeing a dermatologist for treatment is recommended. Treatment for nummular dermatitis consists of the following:

• Protect your skin from getting scraped, cut, or injured in any other way. A skin injury can worsen nummular dermatitis.
• Hydrate your skin. You can do this by taking a 20-minute lukewarm bath or shower once a day. Within 3 minutes of getting out of the water, apply a moisturizer to your still-damp skin. This helps hydrate dry skin. It also relieves the itch and scaling. Adding bath oil to the water also may help. Beware that some oils can irritate your skin. A dermatologist can recommend bath oil that will not irritate your skin.
• Use medicine as directed by your dermatologist. Medicine prescribed to treat the skin includes corticosteroid ointments and tar creams. These help reduce inflammation (redness and swelling) and itch. If a bacterial skin infection occurs, your dermatologist will prescribe an antibiotic. An oral (by mouth) antihistamine that makes you drowsy can help you sleep.

If you have a bad case or widespread nummular dermatitis, you may need:

• Medicated dressings (bandages).
• Phototherapy (treatment with light).
• Oral antibiotics.
• Systemic (taken by mouth or injected) corticosteroids.
• Bed rest in a cool and moist room. You can keep the room moist with a humidifier.

Outcome

With proper treatment, nummular dermatitis can clear completely. Sores on the thighs, legs, and feet often take longer to heal and tend to leave behind darker or lighter spots.

Some patients’ skin clears within a year. Others have these patches for many years. Sometimes the patches go away and then return. Patches that return after clearing tend to appear in the same place as the first outbreak.

Nummular dermatitis: Tips for managing

To prevent nummular dermatitis from returning once your skin clears, dermatologists recommend the following:

• Moisturize. Apply a moisturizer at least once a day. The best time is just after bathing while your skin is damp. A moisturizer helps trap water in the skin. A dermatologist can recommend products that will not irritate your skin.
• Avoid activities that bother your skin. Anything that dries, heats, or irritates your skin can cause a flare-up. To avoid flare-ups, dermatologists recommend using lukewarm water for showers and baths, getting out of the shower or bath after 20 minutes, and not sitting next to a fire or heater.
• Skip the soap. Using a mild, gentle cleanser to clean your skin instead of soap will help. Soap can dry the skin.
• Use a humidifier. When you heat or air-condition your home, use a humidifier to add moisture to the air.
• Dress for success. You are less likely to irriate your skin if you wear loose clothing. You also should not wear rough fabrics, such as wool, which can bother your skin.

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