Why Are My Breasts Uneven?


As women, we are daily inundated with messaging and imagery that makes us question our bodies. These unrealistic standards of beauty often don’t reflect the realities of women’s bodies, in all their wonderful variety.

This can lead to insecurity, wondering what’s normal, what’s medically concerning. Asymmetrical breasts definitely fall into the category of things many women think of as a flaw that applies only to them. But rest assured: The answer to the question “why are my breasts uneven?” is simply that breasts are often uneven, with one larger breast and one small one!

Uneven Breast Size Is Considered Normal

Indeed asymmetrical or uneven breasts are considered very normal. Have you ever done that trick where you took a picture of your face and mirrored just one side? 

You usually end up with two faces that don't quite look like yours. This is because your face isn’t perfectly symmetrical on both sides. You might have one eyebrow that arches slightly higher, one nostril that flares more. Your jaw may be stronger on one side, or your lips fuller.

It turns out that applies throughout our bodies. Fingers on one hand slightly thicker than the other? One foot slightly bigger than the other? It’s all perfectly normal.

And it applies to your breasts too. They’re not identical twins. They’re more like sisters. They may look alike, but they can also have differences. These differences can include size, nipple, areola etc. These are normal anatomic differences.

What Causes Uneven Breast Size?

So, you might be wondering what causes breasts of different sizes? Well, apart from the answer that we’re all just human and that means we’re not built like perfectly uniform machines, there are some stages of development and reasons asymmetry can come into play with one breast larger or smaller than the other.


Breast development starts during puberty and one breast may grow sooner or faster than the other. Usually the other breast will begin to bud and catch up soon enough, but there may always be a bit of asymmetry after the breasts are fully developed. 

The reason one breast grows faster than the other is unknown. It may have to do with the number of breast tissue cells on one side. Or it may be that certain cells respond more quickly to the hormones that play a role in breast development.

Hormonal Changes

Throughout the course of your life, hormone change can result in changes to the size of your breasts. This can include stress, taking hormonal birth control etc.

There are also hormonal changes as you go through your menstrual cycle, especially during ovulation and menstruation. These changes may not affect both breasts equally and you may notice breast asymmetry becomes more noticeable with these changes.


Of course, there are also significant hormonal changes during pregnancy. These changes affect the breasts as your body prepares for breastfeeding. By six weeks into pregnancy, many women's breasts have grown a full cup size or more. And by nine months, the average woman has gained two pounds just in her breasts.

This weight isn’t necessarily distributed perfectly evenly and your breasts may appear lopsided. This may also be more visible to you due to the overall increase in size.

Weight Loss or Gain

Breasts contain fat and so can shrink or grow with weight loss and gain. When you gain or lose weight its distribution throughout the body usually isn’t perfectly even. While we may not notice this with other body parts, it may be more apparent when looking at your breasts.


Breastfeeding can also lead to breast asymmetry, especially if your baby favors one side over the other. Even if you are nursing from both breasts, you may notice asymmetry while breastfeeding. This is because the breast that you just nursed with will be smaller, while the other side will be filling up with breast milk for the next feeding.

When Breast Asymmetry Is Cause for Concern

As mentioned, breast asymmetry is usually considered very normal and may be exaggerated or become more visible at certain times, as listed above.

However, you know your breasts best. And if there’s a sudden growth or change in your breast tissue that results in unevenness, it’s definitely worth seeking medical advice.

This is especially the case if this change is accompanied by any other changes, such as itching, changes to your nipples, fluid discharge from the nipple, changes in the colour of your breast, dimpling or puckered skin, or any lumps.

Some of the conditions that may cause sudden or unexplained asymmetry include:

Benign Breast Lumps

Most breast lumps are benign, which means they're not cancer. Fibroadenomas are the most common type of benign breast lump. 

According to the Mayo Clinic, “A fibroadenoma might feel firm, smooth, rubbery or hard and has a well-defined shape. Usually painless, it might feel like a marble in your breast, moving easily under your skin when examined. Fibroadenomas vary in size, and they can enlarge or shrink on their own.

Fibroadenomas are among the most common noncancerous (benign) breast lumps in young women. Treatment might include monitoring to detect changes in size or feel, a biopsy to evaluate the lump or surgery to remove it.”

Breast Cysts

Breast cysts are common in women before menopause, between ages 35 and 50. But they can be found in women of any age. They can also occur in postmenopausal women taking hormone therapy.

According to the Mayo Clinic, “Breast cysts are fluid-filled sacs inside the breast, which are usually not cancerous (benign). You can have a single or many breast cysts, and they can happen in one or both breasts. They're often described as round or oval lumps with distinct edges. A breast cyst usually feels like a grape or a water-filled balloon, but sometimes a breast cyst feels firm.”

Breast Cancer

Of course, we’ve all learned to be concerned about breast cancer and feeling a lump or noticing sudden growth of one breast might make us all jump to the worst possible conclusion. As mentioned above, most breast lumps are benign. 

However, it’s a good measure to get every lump, bump or change checked out because early detection can be such a difference-maker for those women who do have breast cancer.

breast cancer

What to do About Uneven Breasts

So, you’ve got uneven breasts! Welcome to the gang! Is there anything to be done?

Accept Them!

Our two cents: Accept them and forget about it! Honestly, most of us have asymmetrical breasts. They’re no less beautiful. They’re no less sensual. And no less capable of nursing because they’re asymmetrical. Unequal breasts won't affect breastfeeding or increase breast cancer risk.

Get Fitted for a Bra

Uneven breasts can make it even more confusing to figure out your breast size. So we definitely think getting fitted for a bra is a good idea. A professional bra fitter (in person, or virtually) will know whether you should size up or down, and show you how to adjust your bra so both sides are supported and comfortable.

bra fitting

Consider a Bra “Chicken Fillet” / External Prosthesis

If the unevenness of your breasts really bugs you you can also use removable bra padding or a bra “chicken fillet” to add bulk to the smaller side. Because these are external additions, there’s nothing invasive or permanent about them, but they might give you a confidence boost if this is a source of insecurity! Breast augmentation is a more extreme and permanent solution for changing an asymmetrical breast. If you are considering a breast augmentation, please seek out medical advice.