The cause of pimples on the back of the head may be insect bite dermatitis, sebaceous cysts, folliculitis and so on. 1. Insect bite dermatitis: If you do not pay attention to daily skin protection, or in the environment of mosquitoes, it is easy to be bitten by mosquitoes, which will lead to pimples on the affected area, accompanied by severe itching, if the back of the head by mosquitoes can also lead to the appearance of long pimples. 2. Sebaceous cysts: usually do not pay attention to scalp cleaning, resulting in excessive sebaceous gland secretion, hair follicle blockage, so that secretions can not be discharged in a timely manner, the formation of sebaceous cysts, the disease is more prevalent in the back of the head. 3. Folliculitis: Folliculitis is mostly caused by bacterial infection, manifested as pimples centered on hair follicles, mostly red in color, accompanied by pain and discomfort. If the hair follicles at the back of the head are inflamed, you will also get bumps. It is recommended that patients with bumps on the back of the head should consult a doctor in time to find out the cause of the disease and then treat the symptoms to avoid delaying the condition.