What caused this pruritic labial rash?

For a few weeks, a 36-year-old woman has had this pruritic labial rash.

A potassium hydroxide (KOH) examination revealed evidence of a dermatophyte infection (tinea cruris, A), which is more common in men but does occur in women. A KOH examination or a culture is necessary to exclude the other conditions in the differential and to make the diagnosis. If necessary, a biopsy would also confirm the diagnosis. This patient was successfully treated with a topical antifungal cream.