Mammary gland development during puberty in males is one of the types of physiologic male breast development, which is characterized by an abnormal increase in the stroma and ducts of the male mammary gland, an increase in the shape of the mammary gland, and the ability to clinically palpate breast tissue under the areola, with a diameter of greater than 2 centimeters. Mammary development in pubertal boys is often the earliest manifestation of pubertal development. The exact mechanism is not known. Plasma estradiol reaches adult levels before blood testosterone reaches adult levels in boys, thus the estrogen-to-androgen ratio increases with, but there is a mean higher blood estradiol. During the pubertal stage, localized aromatase action in the mammary gland is enhanced, and excessive local estrogen formation results in pubertal mammary gland development. Mammary gland development in pubertal boys is remarkably self-limiting. Mammary gland development decreases with the process of pubertal development, generally stops at about 20 years of age, and gradually subsides before pubertal development is completed. If a boy develops mammary glands, it is recommended to go to a regular hospital for examination and cooperate with the doctor’s treatment.