An erection of more than 13cm is the normal length, and if the erection is less than 13cm, it is the shortening of the penis. The most common causes of penis shortening in young people are masturbation and circumcision. In addition the developmental period sex hormone deficiency can also lead to penis short. There are also people who are congenital, such as chromosomal abnormalities, which can also lead to penis shortening. If young people are caused by masturbation and circumcision, they must be circumcised as soon as possible during the development period and quit masturbation as soon as possible, and they can continue to develop during the development period, and generally the penis will develop until they are about 18 years old. If the adult penis is short, there is nothing too good drug treatment, can only do surgery, but surgery may lead to impotence, must be done carefully.