Acne on the shoulder may be caused by folliculitis, infectious molluscum contagiosum and other reasons. 1. Folliculitis: when the skin on the shoulder is damaged and irritated, bacteria, fungi and other pathogens can easily enter the skin, thus infecting the hair follicles and triggering folliculitis, which is manifested by the appearance of red papules or mounds on the surface of the skin centered on the hair follicles, and sometimes there are white pustules on the top of the skin, which may be accompanied by itchiness, tenderness, pain and other symptoms. 2. Molluscum contagiosum: Molluscum contagiosum is a skin disease caused by the molluscum contagiosum virus infection, which can appear in any part of the skin except the palms of the hands and soles of the feet, manifested by the appearance of waxy glossy hard hemispherical pimples on the surface of the skin, and generally no itching, pain and other symptoms. Shoulder acne may also have other causes, it is recommended to go to the hospital in time, under the guidance of the doctor for standardized treatment.