16th July 2026

Discoid Dermatitis (Nummular Eczema)

Clinical features

Discoid dermatitis is characterised as single or multiple, itchy, well-defined, coin-shaped, erythematous plaques with +/- vesiculation. It usually involves the lower legs, the forearm and the dorsum of the hand. It commonly affects young women and middle-aged adults. The cause of this is unknown; it is associated with contact allergy manifestation of atopy or localised injury.

Investigations 

• Skin swab – usually shows Staphylococcus aureus colonisation 
• Skin scraping for mycology is useful to rule out fungal infection 
• Patch testing for the suspected trigger as a contact allergy

Management 

• Emollient 
• Avoid allergens 
• Topical steroid 
• Antibiotics if lesion is infected