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As early as the 4th week of the embryo, the magical differentiation of the mammary glands begins. The primitive ectoderm forms paired cord-like primitive mammary glands, which are the “precursors” of the mammary glands. During fetal development, initial mammary glands are formed, producing a simple branched mammary duct structure. At 34 weeks of fetal age, under the influence of estrogen, mammary nodules form behind the areola. After birth, the mammary nodules can persist for 6-12 months before completely regressing. After birth, pseudo-development of the breasts may occur, manifested as breast swelling, and some even can express a small amount of yellowish-white milk. This is because estrogen from the mother’s blood circulation enters the fetal blood circulation, stimulating the development of the fetal mammary glands.
Here, it is also reminded to mothers not to squeeze the newborn’s breasts casually after delivery to avoid infection. This condition generally requires no special treatment, and after a period of time, as hormone levels drop, the baby’s breast swelling naturally resolves.
By puberty, the body secretes estrogen and progesterone, awakening the dormant breasts and leading to mammary gland development. Estrogen stimulates the growth of mammary ducts and fibrous fatty tissue, while progesterone stimulates the development of mammary lobular tissue and the areola. Breast development is the earliest secondary sexual characteristic and marks the beginning of girls’ puberty. Having a pair of full and beautiful breasts can boost a girl’s confidence.
Girls generally begin breast development between 8 and 13 years old, with an average age of about 11. The development on both breasts may sometimes be asynchronous, often with one breast developing 1 to 2 years earlier than the other. The timing and speed of breast development also vary among individuals.
The process of breast development is like a small seed slowly sprouting, flowering, and growing. Medically, the development of the reproductive system during puberty is divided into 5 stages according to secondary sexual characteristics for clinical assessment, known as the “Tanner stages.”
Let’s look at the Tanner stages of mammary development during puberty:
Tanner Stage 1
Ages 5-8, before puberty, only nipple elevation is present, with little difference between boys and girls’ breasts.
Tanner Stage 2
Ages 8-10, breast development enters the breast bud stage, with enlargement and elevation of the nipple and areola, and the appearance of the breast bud. When touched, there is a small, button-like lump behind the breast—remember, this is the breast bud, like a seed that will develop into mature breasts; do not squeeze it!
Tanner Stage 3
Ages 10-13, the nipple and areola continue to enlarge, the color of the areola darkens, and the nipple and breast lie in the same plane.
Tanner Stage 4
Ages 13-15, also called the areola mound stage. The areola protrudes beyond the breast mound, and the breast development is basically formed.
Tanner Stage 5
Around age 15, mature breast stage; the nipple and areola lie in the same mound plane, and the breast is basically fully developed.
If by age 13, there is no obvious breast development, it indicates delayed breast development. There is no need to worry too much because individual differences exist. Nutrition can be enhanced by eating foods that promote mammary development, such as papaya, legumes, fish, meat, and fresh milk. Sometimes during puberty, a clear watery nipple discharge occurs, mostly due to ductal expansion, which usually resolves on its own with no cause for concern. However, if bloody discharge appears, it is necessary to consult a professional doctor promptly to rule out breast disorders.
Contributed by | Mammary Department | Yu Jinling
Original title: “Initial Mammary Development, Attention Moms”