These lesions can be dry or exudative. It is a chronic condition with relapse and re-occurrence often at the same sites. Lesions wax and wane with changes in environmental conditions - worsen in the winter, in low relative humidity, and in the presence of heaters. It is usually diagnosed clinically, and is distinguished from generalized patchy dermatitis, which has ill-defined borders.
Nummular dermatitis is a condition confined to the skin.
Nearly all acutely oozing lesions will reveal S. aureus by culture, however, the majority simply reflect superficial colonization. Such non-invasive colonization does not require antibiotic therapy but will be eradicated by relieving the dermatitis with topical steroids. Spreading dermal erythema, tenderness and frank pus are indicators of invasive infection and the need for antibiotic therapy. No racial predilection has been observed. Nummular dermatitis is more common in males.