Breast Asymmetry: Why is One Boob Bigger Than The Other?

Have you ever stood in front of your bedroom mirror, put your hands to your chest and wondered: Why is one of my boobs bigger than the other?

The good news? You’re not alone. More women or people with breasts have asymmetry than don’t. In most cases, the breast size difference is nothing to worry about.

But in some cases, it can be a cause for concern, so if anything feels unusual, it’s best to take a visit to your doctor.

Pink graphic of different shaped breasts

What does it mean to have breast asymmetry?

As we said, most women have breasts that don’t match.

Breast asymmetry can mean one breast has a different volume, shape, position, or even perkiness. It can also refer to differences, like size and colour, of areola and nipples.

What are the common reasons for breast asymmetry?

1. Normal physical variation

As the saying goes, ‘Breasts are sisters, not twins.

The main reason for breast asymmetry? Nature!

Most of our bodies are not symmetrical. Think about your eyebrows, leg length, and even labia. They’re rarely identical, and that’s because they’re not ‘supposed’ to be.

We’re people, not airbrushed dolls. Natural asymmetry is a beautiful part of being human, so try to embrace it.

Breast size difference is also often genetic, meaning that if your mom and grandma have asymmetrical breasts, you probably will, too.

Woman posing in underwear at home

2. Your menstrual cycle

If you have periods, you’ll have experienced hormones' effects on the body.

Breast tissue naturally changes boob size and shape at different points of our cycle.

Additional blood flow and water retention can make them bigger, and breasts are usually larger and more sensitive during ovulation, which can make breast foreplay more pleasurable - or impossible.

As your breasts change through your cycle, so will their level of symmetry and asymmetry.

3. Pregnancy and puberty

Hormones again!

It’s very common for teenage girls to have one boob bigger than the other when going through puberty because breast tissue develops at different rates.

It’s normal for one breast to grow earlier or faster, creating an asymmetrical appearance that might disappear after puberty - or might not! Either way, it’s nothing to freak out about.

Pregnancy and breastfeeding can also cause breasts to alter, And if you breastfeed, your baby’s feeding habits can also change breast size if they prefer one size over the other.

4. An underlying medical condition

A rare condition called juvenile hypertrophy causes one breast to grow significantly bigger than the other.

People with this condition will have asymmetry that it noticeably larger than most others. It can be treated with surgery.

Close up woman touching her breasts

5. Cysts or fibroids

If you regularly check your breasts (which everyone should), you may have felt small lumps or something that feels like a rope.

These are usually cysts, small fluid-filled sacks, or a noncancerous tumour called a fibroid.

These small lumps can grow within your breasts which can cause them to change slightly in shape and size.

While these are mostly harmless, you should get any unusual lump checked by your doctor to be on the safe side.

6. Scoliosisor spine curvature

People with scoliosis may have one side of their rib cage wider than the other, which can create uneven-looking breasts.

In fact, uneven breasts in girls during puberty are a common sign of scoliosis.

7. Rarely, breast cancer

Breast asymmetry is concerning when it happens quickly for no obvious reason or when the difference is great. In these cases, breast size difference can indicate breast cancer or lymphoma, and you should go to the doctor as soon as possible.

Breast health, like vulva health, is important to look after your body.

Woman checking breasts at home

Regardless of whether you have one boob bigger than the other, look after your breasts by performing a self-breast exam every month and getting annual or biennial mammograms, more if you have a history of breast cancer or have an increased risk for any other reason.

In general, breast asymmetry is normal and natural. Show them the care they deserve by getting regular checkups, and learning to love your boobs the way they are.