It’s not a tumor or a cyst… your daughter is getting breasts!

Not too long ago a mother brought her 9 year-old daughter into my office, concerned about a hard bump growing under one of her nipples. “I know she’s supposed to eventually get breasts,” the mom explained, “but it seems a little early.”

She wanted to make sure the bump wasn’t something more serious like a tumor.

In reality, the first signs of breast development can appear as early as 8 years old and that hard bump under the nipple is exactly what you should expect. Here are some other facts about your daughter’s breast development that should help you understand her changing body.

On average, girls’ breasts start developing between the ages of 8 and 13.

Thelarche (Thee-lark-ee) is the medical term for the beginning of breast development and is caused by the release of hormones (estrogen) by the ovaries. The estrogen causes the fat and other tissues in your breasts to accumulate and grow. For 90% of girls, this is the first sign of puberty.

Typically the first sign of breast development is breast buds.

A breast bud is a firm, round, tender and sometimes itchy lump under the nipple. The tenderness of breast buds will go away as the breast continues to develop along with the itchy sensation that comes when skin starts to stretch.

Breast asymmetry is common during breast development.

In many adolescents, budding breasts may not begin to develop evenly. By the age of 18, however, the size difference should be less obvious and although many adult women still report slightly differing breast sizes, it is completely normal!

What to expect after breast buds…

After the first sign of breast buds, breasts will show an increase in size within 4-6 months. On average, it takes about 4-5 years for full breast development after the start of thelarche, with most girls usually fully developed by the age of 18.

As breasts develop, they become rounder and fuller. The areola may get darker and larger and the nipple may start to stick out.

Breast size…

Breast size is largely determined by heredity and breasts come in all shapes and sizes. There is almost no size that is considered abnormal. Because breasts contain fat cells, a girl’s breast size can increase with weight gain.

Just because she has breast buds doesn’t mean she’s getting her period right away.

On average, it take 2-3 years from the start of thelarche (breast bud development) to menarche (first period). If you think your daughter is close, be prepared. Sign up to be notified when our You Got This! starter kit is back in stock and stay tuned to learn more about breasts, puberty and periods.


Dr. Inga Sazan is a Board Certified Pediatrician and a Fellow of the American Academy of Pediatrics. Learn more about her here. If you have any additional questions, please feel free to drop us a note at Chances are, if you are wondering…you’re not alone!