Why Girls Need a Junior Bra - Bust growth begins surprisingly early! -

Japanese / English

The bust of girls in their growth period can change dramatically over a roughly four-year period.
Learn more based on research from Wacoal's Human Science Research Center.

Wacoal's Human Science Research Center measured the changes in bust size of 280 girls from age 4 to 18,
and a total of 4,500 women over the course of 35 years from 1976.
An analysis of the data revealed the following facts on changes in bust size during the growth period.

Three-step changes in shape and firmness over roughly four years

Bust shape and firmness changes in three steps, developing into an adult bust over the course of about four years. Also, the order in which changes take place is the same for everyone.


From what age does bust growth begin?

This cannot be determined by age. Each girl begins to change at different times, and the degree of growth is also different for each girl. Even at the same age, some girls' busts may start to develop, whereas others will not. Although every girl goes through the same three steps, it is impossible to determine the level of bust development from a girl's age.

Bust growth begins more than one year before the first period

Wacoal's research shows that the area around the nipple begins to enlarge more than one year before the first period. Changes in bust growth are closely related to the beginning of the first period, not age. The bust changes dramatically during the roughly four-year time around a girl's first period.

A girl is already at junior step 2 around her first period

Research shows that the bust of a girl around her first period is generally already at the junior step 2 growth stage (enlargement widens).

Everyone is different! The first period can come
between 10 - 15 years old.

Some girls have their first period at 10, whereas others may not have it until 15 years old, showing a large difference between individuals. Because bust development is related to a girl's first period, it is natural for there to be a large difference between individual growth stages.

Bust firmness and softness 〜Indicators of a developing bust〜

During the growth period, a girl's bust will gradually grow firmer, and will be at its firmest in a woman's lifetime by junior step 3. The softness of the bust changes as the mammary gland develops. A bust that has reached peak firmness in junior step 3 will gradually lose its firmness as fat tissues begin to increase. As an adult's bust matures, the softness and shape changes.

The reason for wearing a junior bra is to gently protect the bust during the growth period

The reasons for wearing a junior bra are completely different than that of an adult version.

A girl's bust during the growth stage changes dramatically in shape and firmness during the three steps. Special bras designed for the growth period are made with different features and for different reasons for each step. The reasons for wearing them are completely different than adult bras which form a soft bust.

The role of a junior bra at each step

Junior Bra【Step1】

A bust that is just beginning to enlarge is sensitive,
so delicate nipples must be protected to avoid pain.

The area around nipples that are beginning to enlarge is very sensitive. Nipples can be conspicuous when wearing a gym uniform or other clothes, and can be painful when rubbing against fabric. The step 1 bra is designed to keep nipples from rubbing against clothing and to keep them from being noticeable.

Junior Bra【Step2】

When the bust becomes noticeably enlarged,
it is best to protect it from shaking as it widens.

Failure to wear a bra when bust enlargement widens, causing a distinct boundary line from the body, can cause it to shake. This can make many girls embarrassed when running and cause pain when shaking. Step 2 bras are made to minimize bust shaking so that girls can move around as much as they like, and to protect and support the bust. Make sure to start wearing a bra when her first period comes.

Junior Bra【Step3】

Although shaped like that of an adult, the bust at this stage is still hard unlike an adult, so it needs to be supported without being constricted.

In step 3, a girl's bust looks almost exactly like an adult's, becoming fuller and enlarging outward. A feature of the bust at this stage is that it is as firm as it will ever be in a woman's lifetime. Bras designed to form (lift) an adult's soft bust do not fit just right and can move around, causing discomfort for girls whose bust is still developing. In step 3, choose a bra with a soft wire or stretchy cup materials designed specifically for the growth period, as they help support enlarged, firm busts without constricting them.

Images are for visualization purposes only.

Keep an eye on your girl's growth.

Wacoal's Tsubomi School undergarment classroom is a place where guardians and schoolteachers can talk to experts about girls' growth. In many cases, girls and their families do not notice bust growth, and when other adults notice they become concerned.

For example…
●Other guardians notice a girl's growing bust at a school sports festival (when wearing a gym uniform), and are surprised that it is developed enough to shake. (From a guardian)
●Even if a girl is uninterested in her own bust, boys going through puberty are aware of it. (From a schoolteacher)
●If a homeroom teacher is male, they often don't know whether or not a girl's bust is developing, or can't talk directly to girls about their bust development. (From a schoolteacher)

Many guardians are surprised at how fast their girl's bust is growing compared to the past. Because junior bras are designed to protect and hide the bust, they can be a necessary part of dress and grooming and protecting girls from predators.

It is easy to see through a white t-shirt or gym uniform, revealing the shape of a girl's bust, so some girls hunch over to hide their chest out of embarrassment.
("When I was in junior high I hated when my nipples showed, so I hunched over with my head forward to try and hide them." 16-year-old girl: From a Girl's Body Navigation questionnaire)

Some girls notice their bust but have a hard time talking to their parents about it, worrying on their own, while other girls do not notice anything. Some girls may already want their own bra.

Girls can be relieved if an adult they are close to notices what they are going through. Instead of thinking it is too early for your own daughter to wear a bra, talk with her at home and keep an eye on her growth.