Prolonged itchy acne behind the shoulders can be caused by a variety of reasons, generally consider ringworm, eczema, Malassezia folliculitis and other causes. It is necessary for the physician to take appropriate treatment measures and methods according to the different causes of the patient. 1. Ringworm: caused by fungal infection, can appear on the shoulders and back of the long pimples, accompanied by itching and other manifestations. 2. Eczema: due to allergic factors or exposure to physical and chemical causes and other reasons, can appear on the back of the shoulders long pimples accompanied by itching and other manifestations. 3. Malassezia folliculitis: due to the rich sebaceous glands behind the shoulders, sebum secretion is exuberant, a large amount of sebum stagnation in the follicular sebaceous glands, the formation of sebaceous plugs; local follicular sebaceous glands within the Malassezia bacteria reproduction of large infections lead to. You need to go to the hospital, after a clear diagnosis of the cause of the targeted treatment, you can not randomly use drugs.