The areola also gets bigger and darker and the nipples may stick out. By the age of 17, a girl's breasts will usually be fully developed, although this may take a bit longer. You'll probably notice that you and your friends grow in different ways.
In general, breast development begins between the ages of 8 and 13. A girl's breasts are typically fully developed by age 17 or 18, however in some cases they can continue to grow into her early twenties.
The areola (the circle of different colored skin around the nipple) gets larger at this time. The breasts then continue to grow. Over time, the nipple and the areola will become raised again.
Although many people have inverted or retracted nipples since birth, they can also occur late in life. That is known as acquired nipple inversion or retraction.
The nipple is created with smooth muscle fibers aligned in a circular and longitudinal fashion. The surrounding areola is formed by the ectoderm during the fifth month of gestation. During the final weeks of gestation, the loose fibroconnective tissue stroma increases in vascularity.
Hormonal Changes
Estrogen controls the growth of the ducts, which is why the areolas and nipples tend to get firmer and the ducts more prominent during the middle stages of the menstrual cycle (when estrogen levels are at their highest).
When they reach 6 months, you can start switching the nipples out for size 3, they should also be on bigger volume bottles (typically 8 oz bottles).
Inverted or Flat Nipples. The size and shape of nipples and breasts vary from person to person and can change during the breastfeeding journey. It is common for nipples to gradually change shape, become more elastic and protrude more during pregnancy and while breastfeeding.
How to tell if you have flat or inverted nipples. Flat nipples1 don't protrude very far from the areola (the darker area surrounding them), even when stimulated. An inverted nipple dimples inwards at the centre. It may look like this all the time, or only when stimulated.
Bumps on the Nipples
Your nipples normally become erect when touched or exposed to the cold. The areolas may become more firm as well. During pregnancy, Montgomery glands enlarge in preparation for breastfeeding.
Breasts develop as the hormones estrogen and progesterone are released at puberty. These hormones make the breast tissue grow.
Falling oestrogen levels at the menopause make breast tissue dehydrated and less elastic, so breasts can lose their rounded shape and begin to sag. The change in shape can leave you with nipples that point downwards.
Just like with breasts, there's no one way that nipples are supposed to look. Both nipples and areolas (the circular skin around your nipple) come in different sizes and colors, from light pink to brownish black. The color of your nipples usually relates to your skin color.
Some women even have flat and inverted nipples which are normal. Due to the hormonal change during puberty, pregnancy, and menopause, there may be nipple appearance and sensitivity changes. Any sudden, noticeable changes in the nipple should be consulted as soon as possible.
When they are stimulated either by touch, cold temperatures or sexual arousal, they harden (actually become erect) and part of that response is for the brown part (the areola) to shrink and wrinkle. It is kind of like a muscle contraction.
Fortunately, within a few months postpartum, most nipples return to their original appearance.
Stimulating, caressing or simply holding breasts sends nerve signals to the brain, which trigger the release of the 'cuddle hormone' called oxytocin, a neurochemical secreted by the posterior lobe of the pituitary gland in the brain.
Breast development in girls is considered delayed when breasts don't develop by age 13. The commonest cause of the delay is that it runs in families. Another common cause of delayed puberty in girls is lack of body fat. Being too thin can disrupt the normal process of puberty.
Globally, a natural female breast has an average size somewhere between a large "A" and a smaller "B" in the US size system. According to European or Australian classifications, this would be a "B".