As girls mature and go through puberty, breasts are one sign that they're leaving girlhood and entering a new stage in life. And once they have breasts, they’ll probably want to wear a bra. Find out how breasts grow, how to measure for a bra, and what kind to get.

When Do Breasts Start Growing?

Breasts can start growing as early as age 8 or as late as 13. Some girls' breasts grow slowly and others grow quickly. Some girls may feel like their breasts will never start growing. But girls start developing at different ages and different rates. One girl might have more developed breasts at 12, while her friend is still waiting.

Stages of Breast Development

Breast development happens in stages. The first stage starts during the early part of puberty, when the ovaries enlarge and estrogen (ESS-truh-jun), an important female hormone, begins to circulate in the body. Doctors often refer to the early stages of breast development as "breast budding."

A breast bud is like a small raised bump behind the nipple. After breast budding happens, the nipple and the circle of skin around the nipple (called the areola) get bigger and a little darker. Then the area around the nipple and areola starts to grow into a breast.

As breasts keep growing, they may be pointy for a while before becoming rounder and fuller. For some girls, one breast might be a little bigger than the other one. A girl's breasts may continue to grow during the teen years and even into the early twenties. Fully developed breasts come in all shapes and sizes.

What Do Breasts Do?

Girls have breasts so they can do an important job later in life. Someday, if they grow up to have a baby, breasts can provide the milk the baby needs. Breast milk is the very best food for babies and mom is the source. And it doesn't matter if those breasts are small, medium, or large. All sizes can make enough milk to feed a baby.

Getting a Bra

Once a girl has breasts, a bra is a good idea, especially when exercising and playing sports. Bras can protect breast tissue and keep the breasts supported. Some girls may also like that bras smooth out their silhouettes and make them feel more comfortable. A bra can make a girl feel better when she's wearing a light shirt, such as a T-shirt.

It can be tough for girls to get up the courage to tell a parent that they need a bra though. If they’re nervous about buying bras in a local store, suggest ordering a few online first.

Like anything new, it can take time to adjust to wearing a bra. Bras can be hard to fasten and adjust. When a bra is on, it can bag or gap, ride up, dig in, or pop open. The straps can slide off the shoulders or dig into them. And a bra can peek out of clothing.

What About Bra Sizes?

Getting the right size bra can make wearing one easier. For instance, a bra that's the right size won't pinch, gap, or slide around. So it makes sense to spend some time learning about bra sizes.

Chest & Cup Size

There are two parts to a bra's size: the chest size (also called the band size) and the cup size. The chest or band size is represented by a number (32, 34, 36, etc.) and is the part of the bra that runs across a girl's chest and around her back. The cups are the parts of the bra that hold the breasts and come in letter sizes (AA, A, B, C, etc.).

Bras come in many sizes, which are different combinations of the chest sizes and cup sizes — 32AA or 34C, for instance. It's important to get both the chest and cup sizes right to ensure a proper fit. Some bra makers now also offer cup options in half sizes to help get a better fit.

How to Measure for a Bra

Getting measured can help girls find the correct bra size. People who work in the bra departments of stores can help with this measurement. Or it can be done at home. Here's how:

• Run a tape measure just under the breasts, all the way around the back and ribcage. The tape measure should rest flat on the skin and lie straight across the back — not so tight that it digs in, but not so loose that it sags down in the back.
• Make a note of the measurement. That's the chest size. Some brands have you add a few inches to this number.
• To measure cup size, take the tape measure around the body across the fullest part of the breasts.
• Write down this number and subtract the chest measurement from it. The difference between the numbers is a way of figuring out the cup size. If the difference between the two numbers is less than 1 inch, the cup size is AA. If it's 1 inch, the cup size is A; 2 inches is a B; 3 inches is a C, and so on. For instance, if the cup measurement was 33 and the chest measurement was 32, that's a 1-inch difference. The bra size is 32A.
• If the chest measurement comes out as an odd number (like 31 inches or 33 inches), it's best to round down to the next number. Most bras have a few sets of adjustable hooks and eyes for adjusting the tightness. It's a good idea to round down, rather than round up, because bras tend to stretch over time.

What Kind of Bra to Buy?

Sports Bras

Many girls' first bra is a sports bra, a type of bra worn by active women of any age. Sports bras prevent breasts from jiggling around when playing sports or exercising. Because they're flatter in the cup area, sports bras also make good first bras for many girls. In fact, because of sports bras, and dresses and tops that have built-in bras, a girl might not need a more traditional bra early on. Not all sports bras are alike, so it’s important to try on a few to figure out which ones feel best.

Other Kinds of Bras

Besides sports bras, there are a lot of other types of bras. The most natural-looking bra is a soft-cup bra, which doesn't do much to change the shape of the breasts. Soft-cup bras come in different fabrics and thicknesses and some may have an underwire. An underwire is a U-shaped wire inside the fabric that goes under the breasts to help support them. If breasts are a C cup or larger, an underwire bra is a good choice.

Other bras may have more structured cups and some come with padding inside. Minimizer bras are also available for anyone who wants their breasts to appear smaller. These bras are usually made of thicker fabric with bigger backs and straps.

What Else Should I Know?

Some girls may wonder how they can make their breasts grow faster or bigger. There isn't any magic cream or pill that can speed up the process or make breasts larger than they are. In fact, heredityand weightmostly determine breast size. So if a girl's mom or sister has big breasts or small breasts, she might develop breasts of similar size. And a girl who has more body fat is more likely to have larger breasts.

Breasts are just one sign that a girl is getting older and on her way to becoming a woman. Encourage your child to come to you with any questions or concerns about breasts or bras. Your doctor is also a good source of information on breast growth.