Breast development is a normal part of growing up for girls. Children can enter puberty as early as 8 years old, though many children tend to begin the transition closer to the age of 12 or 13. The existence of breasts can be either a source of excitement or embarrassment; emotions at either end of the spectrum are normal, but both can lead to changes in self-image and self-confidence. Breast development may be seen as a part of growing up, but the roots of the process develop well before a child is born.
In-Utero Development
According to Boston's Children's Hospital, the female breast is already well-developed before a baby girl is even born. The mammary ridge, a thickened section in the chest wall that's also called the milk line, forms in the sixth week of fetal development. The starting point of the nipples and the milk duct system through which the milk travels before it's expressed are all in place before birth.
Puberty and Breast Development
The breast changes that accompany puberty in girls occur in several stages. The nipple becomes raised before a girl goes through puberty, according to the New York-Presbyterian Morgan Stanley Children's Hospital. The breasts begin to grow larger, starting with small buds, when estrogen rises prior to the onset of menstruation. The development of a female child's breasts is a gradual process; the buds appear, leading to the enlargement of the nipple and areola, followed by a rounding of the breast mound and the raising of the nipple. The secretory glands in the breast that are connected to the milk ducts form once a girl has begun to ovulate.
Size and Appearance
The size of a girl's breasts varies per person, just like other physical characteristics, and may be linked to genetics. MassGeneral Hospital for Children explains that having breasts of different sizes is not uncommon during adolescence. The size discrepancy often resolves itself over time, and is rarely a cause for worry. Girls who have very small breasts but are otherwise heading into puberty normally with the development of secondary sex characteristics, such as pubic hair and menstruation, need not be concerned about their appearance or development.
Abnormalities
Girls whose breasts do not enlarge during puberty may lack glandular tissue, or mammary glands. This condition is quite uncommon, but may be something to look for if other signs of puberty are progressing during a normal time frame. Other abnormalities in a female's breast development include the presence of additional milk lines and nipples that could appear later in life during a pregnancy.
Breast Development in Boys
An enlargement of the breast tissue in boys is called gynecomastia, and is common at birth and again during the early teenage years. MayoClinic.com explains that the female hormones circulating through a baby boy's body directly after birth can cause the temporary swelling of the breasts, a condition that resolves itself within a few weeks after birth.
According to MassGeneral, the majority of adolescent boys, up to 70 percent, experience a swelling of the breasts to some degree during puberty due to the fluctuation of hormones. In most cases, the breast tissue recedes on its own without treatment. Boys who are overweight may be encouraged to eat healthily and exercise to shed weight, as fat tissue in the chest may make it appear as if the breasts are enlarged, though the cause in this case has nothing to do with hormones and is not an abnormality associated with glandular or breast tissue.
