Minimal puberty (mini-puberty, or minipuberty), is found in the medical gonadal stabilizer doctrine. This theory suggests that the negative feedback link between the hypothalamic-pituitary-gonadal axis (HPGA) is established in the newborn and early infancy, but its inhibitory function is not yet mature. At this time, gonadotropin (Gn) is secreted at a high level that can resemble puberty, so it is called “micro puberty”. After one year of age, the threshold of negative feedback changes, sensitivity increases, and its negative feedback effect gradually strengthens. 3 years old to prepubertal is highly sensitive, GnRH secretion is inhibited, and Gn is at a low level. On the eve of puberty, the threshold of negative feedback increases, sensitivity decreases, and GnRH secretion by the hypothalamus and Gn secretion by the pituitary gland begin to increase. After puberty, the frequency and amplitude of GnRH release increases significantly, and the pulsatile secretion of LH and FSH increases contributing to gonadal development. At birth, the hypothalamic-pituitary-gonadal (testicular or ovarian) axis, as one of the important endocrine regulatory systems in the body, is not yet as stable as in adults, but it has basically completed its establishment. Before birth, this system is temporarily put on hold in the mother’s body due to the large amount of estrogen produced by the placenta. After birth, as the umbilical cord is cut, the fetus loses its connection to the mother and the fetal endocrine system must begin to learn to carry the burden alone. Soon after leaving the mother’s body, especially in male infants, within minutes, they begin to commission the operational functions of their reproductive endocrine system, secreting androgen levels up to the low end of normal adult male levels. At this time, the testicles are mildly enlarged, there is penile erection, and even a transient manifestation of a little facial acne, which can last until about half a year of age; compared to male infants, female infants are a little slower to respond, but they also start to adjust their reproductive endocrine system within a few hours. At this time, this system is not yet very stable and can produce estrogen intermittently. During this time, estradiol levels can fluctuate between 0 and 50 pg/ml (equivalent to the lower limit of estrogen levels in normal adult women). Some female infants who are sensitive to estrogen may show more pronounced breast development. Due to fluctuations in estrogen levels, a very small number of infants may even experience a little bleeding similar to menstruation in adolescent girls. These manifestations are usually short-lived and not very pronounced, but can occur before the age of 2 years. This manifestation in infancy is extremely similar to the process of true puberty. Therefore, the medical term for it is “micro-puberty”. Micro-puberty can be seen as a small preview of the real “big” puberty a few years later. The actual meaning of micro-puberty is not well understood, and its manifestations vary from person to person. It is often overlooked, but it is indeed a physiological phenomenon that exists early in our lives. In fact, not all breast development in young children is precocious sexual maturity, most of them are just a special manifestation of secondary sexual characteristics, a developmental variation and a self-limiting condition, called simple breast development in children, which is a kind of partial precocious sexual maturity. According to the statistics of Zhejiang Children’s Hospital, there are about 1,000 cases of simple premature breast development every year, which is a relatively high incidence compared to the 1.2 million babies seen in Zhejiang Children’s Hospital every year. Simple premature breast development is a relatively common phenomenon among infants under two years of age, and most children will heal on their own, and does not cause the sexual maturity that everyone thinks it does. Sexual maturity can be divided into four stages, two-year-old infants are in the “small adolescence” Why is it easier for small infants under the age of two to have simple breast development? Because this is the period when babies are in a small adolescence. Sexual maturity can be divided into four stages: fetal, perinatal, childhood, peri-pubertal and adolescent. During perinatal infancy, which can be referred to as microadolescence, the hypothalamic pituitary gonadal axis, the organ that controls the development of human sexual characteristics, is not yet well developed, and the gonadal axis of some babies is in an active state, making them prone to an increase in estrogen and follicle-promoting estrogen in the body, which leads to breast enlargement. Most babies will stop developing after the age of two, but if they continue to develop, they must seek medical attention. Most children will heal on their own after the age of two, so parents can rest assured. However, there are some children who do not heal on their own, and if the child’s breasts continue to grow after the age of 2, it is important to pay attention to the possibility of true precocious puberty. The division of labor in medicine is becoming increasingly refined, and not only do general surgeons not know the true definition of precocious puberty, but even pediatricians do not know much about the concept of micro-puberty. Therefore, some doctors will simply determine precocious puberty after seeing the baby’s breast enlargement. During this period, some babies’ hypothalamus-pituitary-gonadal axis is in a temporary “activation state” and “negative feedback regulation” is not yet sound, so when they are slightly stimulated by the outside world, such as abnormal mood, they will appear. The hypothalamus-pituitary-gonadal axis does not respond to the temporary fluctuations of specific sex hormones, such as abnormal moods, which can lead to breast enlargement. Because the hypothalamic-pituitary-gonadal axis enters a resting phase after the age of 2 years and until puberty is initiated, it is highly sensitive to negative feedback from sex hormones, which inhibits the rise of sex hormones. Most of the breasts that began to enlarge during infancy will gradually soften and even disappear at this time.