CHANGE

Breast development

Changes in your breasts are one of the first signs of puberty. It might feel unfamiliar. Sometimes it's sore. Sometimes it feels sensitive to the touch.

It's also common for development to happen at different rates. One breast might start to grow before the other. Behind the nipple, you might feel a small, firm lump. This is part of the development and completely normal.

It's a phase that all girls go through

Breasts beginning to change is one of the first signs of puberty. It can feel unfamiliar. Sometimes it's sore. Sometimes it feels sensitive to the touch.

It's also common for development to happen at different rates. One breast might start growing before the other. Behind the nipple, it might feel like a small firm lump. This is part of the development and completely normal.

It's a phase that all girls go through.

Breast size – what determines it?

Breast size is affected by:

  • Genetics – inherited traits from parents and relatives.
  • Amount of fatty tissue – people with more body fat may have larger breasts.
  • Hormone levels – the amount of estrogen affects development.
  • Age – breasts can grow even after puberty, e.g., during pregnancy or weight gain.

When do breasts start to grow?

Typically between 8–13 years of age. The first sign is often a small lump under the nipple, called a breast bud.

When should I be concerned that my breasts haven't started to grow?

If no signs of puberty (no growth spurt or pubic hair either) are visible by the age of 13, it may be advisable to contact your health center for an assessment.

When do breasts stop growing?

Usually around 16–18 years old, but small changes can occur throughout life, for example due to weight changes, pregnancy, or hormonal shifts.

What happens when breasts start to grow?

  • A small lump (breast bud) forms under the nipple.
  • The area may feel tender or swollen.
  • The nipple and areola may darken and become more prominent.

Are there different phases as breasts grow?

Yes, according to the Tanner scale (5 stages):

  1. Flat breast (before puberty).
  2. Breast buds form.
  3. Breast and areola grow.
  4. Areola elevates and forms a separate contour.
  5. Fully developed breasts.

How long do you only have a swollen nipple?

The breast bud stage can last a few months up to a year before the breast grows further.

Why does the nipple swell and feel sore?

This is because glands and fatty tissue grow and blood flow to the area increases. Hormones make the tissue extra sensitive.

How long will my breasts be sore?

Soreness is most common during the first months of development, but tenderness can come and go throughout puberty.

Where do I turn if I have questions about my breast development and puberty?

You can contact your school nurse or a youth clinic yourself.
If you prefer your parents to be involved, you can either contact the school nurse or the health center.

I'm the first in my class to develop breasts – what should I do?

It's normal to develop early. All bodies have different timelines. It's a good idea to:

  • Wear a bralette or soft bra for support.
  • Talk to an adult about questions and feelings.
  • Remember that it doesn't mean you're "older" than you are – just that your body has started its development.

I’m the last in my class to develop breasts – what should I think?

Late development is also normal. Puberty often starts within a year or so. In the meantime:

  • Remember that it says nothing about who you “are as a person.”
  • Focus on things you enjoy doing.
  • Know that you will develop at your own pace.

Different breast sizes

It's completely normal for breasts to be different sizes – in fact, the majority of women have some difference between their right and left breasts.

The most common reasons are:

  1. Natural asymmetry
    The body is rarely completely symmetrical. Just as one foot or hand might be slightly larger, one breast can be larger than the other.
  2. Different growth rates during puberty
    Breasts develop in different stages, and it's common for one to develop "ahead" of the other by several months or even years. Often, this evens out over time, but not always completely.
  3. Hormonal fluctuations
    During the menstrual cycle, pregnancy, or breastfeeding, one breast may swell more than the other because hormonal effects and fluid retention do not always occur exactly equally on both sides.
  4. Difference in glandular tissue and fat distribution
    Breasts consist of both glandular and fatty tissue, and the proportions can differ between sides.
  5. Habits and movement patterns
    Sleeping position, posture, or carrying heavy bags on one shoulder can slightly affect the shape and position of the breasts over the long term.

💡 When should you get it checked?

  • If the difference appears suddenly
  • If you notice a lump, skin retraction, or changes in the nipple
  • If the breast becomes red, swollen, or tender in a new way