The usual sites are the chest and mantle and the upper arms. The history often suggests a hot, humid environment as a precipitating cause. Once established the condition tends to persist or recur over a prolonged period. The biopsy is not diagnostic. Patch testing or a KOH wet mount may be done to investigate possible allergic contact dermatitis or Pityrosporum folliculitis.
Histologic examination reveals superficial spongiotic dermatitis associated with a hair follicle.
This finding is not specific. Cooling soothing emollients have been used for 30 years with variable success. Corticosteroids have not been demonstrated to be effective. Recently PUVA therapy was reported to be successful. Although unfamiliar to generalists, dermatologists should recognize this condition.