The causes of a large and small scrotum in newborns mainly include the following: a. Physiological phenomenon, because the left and right sides of the normal human body are not absolutely symmetrical, so a slight large and small scrotum is a normal phenomenon and does not need to be dealt with. If a newborn baby has testicular dysplasia on one side, the scrotum will also appear as one big and one small. In this case, you can wait and observe, and in many cases it will heal on its own. If one side of the newborn’s testicle does not descend into the scrotum, it will also cause a large and small scrotum, which should be treated by surgery in time.