Papulo-pustular acne limited to the back or upper trunk with no involvement of the face is rare. In the presence of comedones, the diagnosis of acne may be easily made. However, comedones may be missing, making the diagnosis of acne somewhat difficult without histological evaluation. This is especially true if the onset of the eruption is delayed beyond the acne age. In such cases, the differential diagnosis would include bacterial and Pityrosporum folliculitis, and eosinophilic folliculitis. Acne is strongly suspected in the presence of nodular/cystic lesions.

Unlike cases of facial eosinophilic folliculitis, those with trunk involvement are much more likely to have associated immunosuppression. Lesions tend to be pruritic and pustules may decorate the border of an annular plaque. In HIV-positive individuals, lesions of eosinophilic folliculitis often are difficult to distinguish from the so-called papular eruption of HIV disease. Some authors believe that the two disorders may be related or may coexist based on examining multiple biopsies from the same patient.