The cause of acne on a man’s back may be Malassezia folliculitis or acne. The causes need to be analyzed according to different diseases. 1. Malassezia folliculitis: this disease is caused by Malassezia follicular inflammatory damage. If glucocorticoids or broad-spectrum antibiotics are used for a long period of time, Malassezia follicularis can proliferate in the hair follicle, producing free fatty acids, causing sebum retention, and the stimulation of free fatty acids leads to the dilation and rupture of the hair follicle, resulting in the release of hair follicle contents into the surrounding tissues, resulting in an inflammatory reaction. 2. Acne: Acne is a chronic inflammatory skin disease of the sebaceous gland units of hair follicles. Heredity, androgen-induced sebum secretion, keratinization of follicular sebaceous gland ducts, propagation of Propionibacterium acnes, and immune-inflammatory responses may be associated with it. In some patients, the onset of the disease is also influenced by genetic, immune, endocrine, emotional and dietary factors. There may be other reasons for men to have back acne, so it is recommended that the patient go to the hospital in time and follow the doctor’s instructions for reasonable treatment.