A fungal disease of the skin other than of the scalp, bearded areas and feet, characteristically appearing as flat, spreading, ring-shaped or circular lesion with a characteristic raised edge around all or part of the lesion. This periphery is usually reddish, vesicular or pustular, and may be dry and scaly or moist and crusted. As the lesion progresses peripherally, the central area often clears, leaving apparently normal skin. Differentiation from inguinal candidiasis, often distinguished by the presence of “satellite” pustules outside the lesion margins, is necessary, because treatment differs.

Presumptive diagnosis is made by taking scrapings from the advancing lesion margins, clearing in 10% potassium hydroxide, and examining microscopically or under UV microscopy of calcofluor white preparations for segmented, branched non-pigmented fungal filaments. Final identification is through culture.