A lump inside the male nipple is mostly considered to be gynecomastia, which is common in adolescence and old age. The main manifestation is an enlarged breast on one or both sides, or a disc-shaped lump under the areola, with okay borders, sometimes with pain or pressure, and rarely with the possibility of malignant transformation. Most male breast development disorders belong to the physiological period, or due to the hormonal imbalance in the body. In adolescence, because the testicular function has not yet reached its peak, the androgen level is not high, and the relative estrogen level is high, which can lead to mammary gland development. Older patients or patients with liver disease have decreased androgen levels and poor estrogen inactivation, which can also lead to an imbalance of sex hormones causing mammary gland development. Male breast development does not require special treatment. If you find that the lump gradually increases in size or is accompanied by significant pain, you can go to the hospital to see a doctor.