Nummular dermatitis is characterized by chronic or relapsing itchy coin-sized ovoid-shaped red plaques.^[3][4] They can occur on the trunk, limbs, face, and hands.^[1][2][5]

Many contact sensitizers or irritants are known to cause contact dermatitis superimposed on nummular dermatitis. Studies have implicated nickel, cobalt, chromate, and fragrance as likely culprits.^[6][7] Xerosis, or dehydration of skin is also a likely cause.^[8] Infection with Staphylococcus aureus bacteria or Candida albicans may also play a role.^[8]

Diagnosis of nummular dermatitis is largely via clinical observation. Biopsies are typically not necessary, and cannot be used to rule out other atopic dermatitis or other eczemas.^[9][10] However, patch testing may be employed to rule out irritants (contact dermatitis) as a cause.^[6][11] In children, nummular dermatitis is commonly confused with tinea corporis.^[8]

One of the keys to treatment and prevention involves keeping the skin moisturized. Lotions, creams, and bath oils may help prevent an outbreak. If the condition flares up, a common treatment involves the application of topical corticosteroids. Oral antihistamines may help lessen itching. Avoidance of irritants is a common strategy. More severe cases sometimes respond to ultraviolet light treatment. If the condition occurs only during the sun-less winter months then vitamin D supplement might be an effective treatment.^{[citation needed]}

The prevalence of nummular dermatitis in the United States is approximately 2 per 1,000.^[12] It is considered a disease of adulthood, for it is rare in children.^[13]

• List of cutaneous conditions
• Sulzberger–Garbe syndrome