A pimple on the private part of a boy may be caused by genital herpes, scrotal eczema, folliculitis and other diseases. 1. Genital herpes: the main pathogen of genital herpes is the herpes simplex virus, and the triggering factors include low immunity, skin injury, and exertion. Patients will appear around the genital blisters, ulcers, tingling and other symptoms, the initial manifestation of the private part of the boy grew a “pimple”, and then may continue to develop as a cluster of blisters. 2. Scrotal eczema: the cause of scrotal eczema is not yet clear, it may be due to abnormal immune function, heredity, nerve tension and other factors. Patients will appear in the scrotum skin itching, small blisters, pimples blisters and other symptoms, manifested in the private part of the boys grew a “pox”. 3. Folliculitis: folliculitis may be mainly due to hair pulling, skin trauma, sweating, wearing tight clothes and other factors. The patient manifested in the skin long red pimples, itching, pain, etc., will appear boys on the private part of the growth of a pimple situation. There are many causes of a pimple on the private part of the boys, need to be before the hospital, to identify the cause.