Acne on the back can be caused by acne and folliculitis. 1. Acne: It is related to the exuberant secretion of androgen, as well as the reproduction of Propionibacterium acnes in hair follicles and the large secretion of sebum. It can lead to pimples, inflammatory papules, pustules, and nodules on the face and chest and back, which may lead to back acne. 2. Folliculitis: Hair follicles on the back secondary to bacterial infection or fungal infection, common as Staphylococcus aureus, Malassezia, etc., may cause the hair follicles to appear red pimples, surrounded by a red halo, can also lead to the symptoms of back acne. There may be other reasons for back acne, so it is recommended to go to the hospital for examination and treatment as prescribed by the doctor.