The redness and swelling of the lower part of the boy’s body is considered to be caused by trauma, circumcision, scrotal infection and other reasons. 1. Trauma: due to external impact, extrusion, etc., the formation of hematoma caused by the lower part of the red and swollen situation. 2. Circumcision: mainly due to the foreskin is too long and adherent to the penis, urine stimulation, dirt accumulation, the formation of circumcision, infection of the foreskin and the head of the penis inflammation, usually manifested in the lower end of the foreskin redness and swelling, pus oozing. 3. Scrotal inflammation: due to the infection of the scrotum, the scrotal skin appears inflammatory reaction, under the stimulation of inflammation, the lower part of the boy appears red and swollen. There may be other reasons for the swelling of the lower part of the boy, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.