Breasts begin to develop in utero, starting from a thickening in the chest region known as the mammary ridge or milk line.
More specifically:
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Fetal Development: The development of breasts initiates during fetal development. The mammary ridge, a band of thickened tissue, appears on the chest. This ridge is the precursor to breast tissue.
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Nipple and Duct Formation: By birth, a baby girl has already developed nipples and the beginnings of the milk-duct system. These structures form as part of the early stages of breast development.
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Lifelong Changes: Breast development doesn't stop at birth. Breasts continue to change throughout a person's life due to factors like puberty, menstruation, pregnancy, breastfeeding, and aging. These changes impact the size, shape, and composition of the breasts.
The "start" of a breast isn't a singular point but rather the initiation of a developmental process during fetal growth.
