Pimples behind the ears may be caused by folliculitis, boils and sebaceous cysts. 1. Folliculitis: it is a disease in which the hair follicles are mainly involved, the cause of which is mainly related to bacteria and other pathogens. The clinical manifestation is a red papule or pustule centered on the hair follicles, which is easy to occur in the head, face, neck and shoulders, etc. Some patients may have the symptom of pimples behind the ears. 2. Boils: acute purulent inflammatory disease of the hair follicles and surrounding tissues, the cause is mostly caused by Staphylococcus aureus infection, the patient manifests one or more slightly elevated nodules, with pus in the center, which can occur in any part of the body, and the more common parts of the head and face, buttocks and other parts of the body. 3. Sebaceous cysts: sebum accumulation to form retention cysts, is a benign skin disease, its cause is mainly due to the follicle sebaceous gland mouth blockage. Sebaceous cysts are mostly round, the volume can be large or small, and are found on the head and face, back and buttocks. There are many reasons for pimples behind the ears, and patients are advised to seek medical examination to clarify the cause.