Male pubertal breast development is the enlargement of one or both mammary glands caused by benign hyperplasia of the male breast tissue. Gynecomastia is a very common clinical phenomenon and can be seen in the neonatal period, adolescence, and adulthood. The main focus is on male breast development during puberty. It usually occurs between 12 and 16 years of age, with a peak incidence between 13 and 14 years of age. The prevalence is 22.2% to 69%. The enlarged breast tissue is usually no more than 3 cm, may be asymmetrical and mildly painful to the touch, and may last 12 to 18 months. The majority of the enlarged breast tissue gradually shrinks to disappear by the age of 20 years as male sexual development matures, while a few persist for a long time. Gynecomastia during puberty is mainly caused by the relative imbalance between androgen and estrogen levels. The absolute or relative elevation of estrogen levels and the decrease in free androgen synthesis are either due to increased sensitivity of breast tissue to normal levels of estrogen. Etiology of male pubertal breast development: 1. testicular tumors and feminized adrenal cortical tumors, patients may be accompanied by gynecomastia. 2. Hypogonadism and androgen insensitivity syndrome and abnormal testicular function due to infection, chemotherapy, and trauma are mostly associated with gynecomastia. 3, the enhanced aromatization of estrogen precursors by extra-gonadal tissues can be seen in a variety of diseases such as obesity, liver disease, hyperthyroidism, congenital adrenocortical hyperplasia, Klinefiher syndrome, etc. 4, drugs can also cause gynecomastia, such as androgens, synthetic steroid hormones, estrogen, chorionic gonadotropin, ketoconazole, digitalis, drugs that inhibit the synthesis of testosterone, etc. 5. Gynecomastia of unknown cause. Diagnosis of male pubertal breast development: 1. First, a careful distinction should be made between gynecomastia and pseudo-female-type breasts. The latter is an increase in the fatty tissue of the breast rather than an increase in the glandular component of the breast. During the examination the patient may feel tenderness and note the presence of breast lumps. 2. Detailed medical history includes: family history, personal nutritional history, growth and development history, time of breast development, and medication history such as synthetic steroid hormones, chorionic gonadotropin and amphetamines. 3. Physical examination: pay attention to the development of secondary sexual characteristics during puberty, carefully examine the size of testicles and the presence of lumps, the presence of feminization signs as well as spider nevus, liver palm, abdominal lumps, etc. 4.Hormone measurement and biochemical examination, including liver function, thyroid hormone, LH, FSH, testosterone and estradiol, androgen value increase is more reliable. 5. Ultrasound of testes and CT or MRI of adrenal glands to exclude tumors of testes, adrenal glands and other tissues. Treatment of male pubertal breast development: Most patients with male pubertal breast development do not require special treatment. It is a common phenomenon that is part of the pubertal development process. Most of them can be relieved naturally to relieve their mental concerns and anxiety, and should generally be reviewed every 6 months. 1.Medication: The treatment effect is related to the duration of the disease, and the treatment is effective for those with the disease duration within 1 year. Commonly used drugs include: androgens, anti-estrogenic drugs and aromatase inhibitors. 2.Surgical treatment: removal of breast tissue. Indications: breast diameter greater than 4, long-term non-receding; obvious enlargement of the breast affects the beauty; drug treatment is ineffective; suspected malignant changes.