Thelarche is when female humans develop full breasts. It happens from about 9–15 years of age today, although in the past it began at age 12. This usually begins when girls are about 9. A lump that is a bit hard appears in each breast under the areola, which is the dark ring around the nipple. The lump in one breast may grow before the other one. This is called breast budding. Within 6–12 months, both breasts will have started growing. The swelling can be felt and seen outside the edges of the areolae. About 1 and a half to 2 years after the breasts first start growing, they are close to the shape and size of an adult woman's breasts. The nipple and areola may be on a smaller mound on each breast. This small mound usually goes away when each breast is fully grown. Breast size depends on the body's amount of fat.
- Olson, Ginny Teenage Girls: Exploring Issues Adolescent Girls Face and Strategies to help them https://books.google.com/books?id=miQ5iJnXDKkC&pg=PT30&dq=girls+breasts+start+growing+10+years&hl=en&sa=X&ei=YhDgVKffF4qmyAT6q4CgDQ&ved=0CB0Q6AEwAA#v=onepage&q&f=false
- Marshall, Human Growth, p. 187.
- Anne Byers (2007). "How do Girls' Bodies Change during Puberty?", Frequently Asked Questions about Puberty. New York, N.Y.: Rosen Publishing, 26–33 at 27. ISBN 978-1-4042-0966-4. .
- Marshall, Human Growth, p. 188.
- See also Normal breast development. 007 Breasts. Retrieved on 2 May 2010.