In order to further explain the reasons why penises are big and small, let's review the occurrence and development of penises together. For the convenience of description, we divide it into four stages: (1) In the first 10- 12 week of pregnancy, the penis just differentiated, only 3.5 mm long, and testosterone was produced under the action of hCG secreted by placenta. (2) In the second and third trimester of pregnancy, the penis grows rapidly, reaching 2.5-3.5 cm at birth. At this time, the fetal pituitary gland begins to secrete gonadotropins LH and FSH. (3) From birth to adolescence (about 7 years old), the penis grows slowly, which is because the hypothalamus and pituitary gland develop slowly and the testosterone level is low. (4) After puberty, the pituitary and testosterone are vigorous, and the penis grows rapidly. It takes only about 5 years to reach the adult level, and the growth becomes thicker. When the hormone level of the elderly is obviously reduced or after surgical castration, the penis can be secondary degeneration. If secondary impotence stops sexual contact for many years, it may also cause pathological degeneration, which is not a problem of using it and discarding it, but the result of smooth muscle fiber degeneration. In short, the differentiation and development of penis depends entirely on the testosterone level in the body. If the testosterone secretion is insufficient in the sixth to ninth month of pregnancy, and the penis development is lower than normal, the penis will become smaller at birth. So, what is a real penis? The penis is shorter than 2.5 cm before puberty and 5 cm after puberty, with abnormal development and no erectile function; Especially secondary sexual dysplasia, sexual dysfunction, infertility and azoospermia. At this time, it can be considered as abnormal penile development. What is the standard of penis? Most young men are curious, and always secretly compare penis size with people around them when taking a bath. Once you find that your penis is shorter than others', you will cast a shadow on your heart, feel ashamed, feel inferior and depressed, and never want to go to the public bathroom or swimming pool again. Is the problem really that serious? To answer similar questions, we must first make clear how abnormal the penis is. Secondly, it is necessary to find out whether it is abnormal development or individual differences within the normal range. Finally, it is also the most important thing that everyone cares about. If the penis is slightly smaller, will it affect normal sexual life? That is, can you make your wife happy? A man's penis is different from his height, fat and thin features, with different lengths and uneven thickness. Shi has measured the penis size of China 14 12 healthy young men and the penis erection length of 126 healthy men. The results show that the longest is 14.5 cm, the shortest is 4 cm, and the average is 8.375 cm. Maximum circumference 12 cm, minimum 4.5 cm, average 8.3 cm. The longest 16 cm and the shortest 12 cm during erection. Maximum circumference during erection 14 cm, minimum 8 cm, average10.75cm.. The penis length of 1000 normal adult males investigated by Liu Guozhen et al. is: the normal length is 4.9 ~ 8.6 cm, with an average of 6.55 cm, the longest is 10.6 cm, and the shortest is 3.7 cm. Wu Weicheng and others measured the penises of 2547 male college students aged 16-40, with an average length of 7.43 cm and an average circumference of 8. 17 cm. The average penis elongation is 13.34 cm, which is close to the calculated erection length 13.08 cm, so the elongation can represent the length after erection. It can be seen that there are some differences in the measurement results of different authors, and the results are also influenced by regions and nationalities. In addition, the penis length of the same person is not constant under normal circumstances, such as tension, cold or severe fatigue, which will shorten the penis. In addition, the measurement methods themselves are quite different, so it is difficult to judge whether the penis is normal simply from the length. Therefore, the above figures can only be used as a reference, and never try to compare your own length. Clinicians are never willing to judge whether it is normal by the length of penis. As long as you can have normal sexual intercourse, it is normal to complete the task of giving birth. Otherwise, this family would have been eliminated.