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Woman consulting with a doctor about why her breasts are uneven.

September 11, 2020 • read

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Why are my breasts uneven?

Endlessly airbrushed images on social media would have us believe that all breasts are evenly sized and shaped. The truth is that about half of women have uneven breasts, known as breast asymmetry in medical terms.

Inspecting your body in the mirror, you might find that your breasts look a tad uneven. Should you be concerned for your health? The good news is that breast asymmetry is not a medical concern in the vast majority of cases. In fact, most women have some degree of breast asymmetry. 

While breast asymmetry is usually harmless, it can sometimes indicate a bigger problem like cancer or a developmental disorder. Pronounced breast asymmetry can also be a barrier to living a normal, confident life. So what does breast asymmetry entail, and what causes it?

What is breast asymmetry?

Breast asymmetry is defined by differences between your breasts. There can be differences in size, shape, volume, density, or position on your chest. 

Most women have slightly uneven breasts, but no one ever notices because the differences are minor. Breast asymmetry becomes tough to conceal when one breast is 20% greater in size than the other.

Having a large size difference can take a toll on your self-esteem. It can also indicate elevated risk for breast cancer. There are many causes for breast asymmetry, and researchers are working hard to better understand the link between embryo development, puberty, and environmental factors. 

What causes breast asymmetry?

Developmental disturbances

Your breasts and their surrounding structures start developing while you’re still an embryo. If any structures are compromised during embryo development, there may be breast asymmetry later on in life. 


Some breast abnormalities are passed down from parent to child. For example, people with Poland’s syndrome, a rare congenital disease, may lack a pectoralis muscle on one side. 

Tubular breasts

Tubular breasts is the name of a condition caused by breasts not developing normally during puberty. One breast may not grow at all, and instead develops a large, puffy areola. The exact cause of tubular breasts is unknown, although scientists have tentatively found a link to your body’s use of collagen.


There are a few types of hormonal breast asymmetry. One occurs when breasts react abnormally to hormones as you’re developing through embryo, infancy, and puberty. In most cases, breast asymmetry occurs during typical hormonal fluctuations over a month or throughout your life. They include:

  • During your menstrual cycle. 
  • Around menopause.
  • During pregnancy or breastfeeding. 
  • When taking hormonal birth control like the pill or patch. 

Breast asymmetry often begins in puberty and can be a difficult experience for girls navigating their early school years.  

Having a baby

Women with no prior breast asymmetry may find their breasts become uneven after going through pregnancy, birth, and lactation. This is due to loss of skin tone and elasticity, as well as hormonal changes. 

Idiopathic factors 

Idiopathic means “No one really knows.” In many cases, doctors can’t pinpoint an exact cause for breast asymmetry in their patients. As long as the patient is in no known medical danger, doctors treat the appearance and side-effects of breast asymmetry rather than worrying about the cause. 

Breast asymmetry and cancer

Even though breast asymmetry is common, it can be a warning sign for cancer if you are a higher-risk patient. High-risk patients meet one or more of the following criteria:

  • Personal or family history of breast cancer. 
  • Obesity and/or a sedentary lifestyle. 
  • BRCA gene mutations.
  • Over 50 years old in age.
  • History of hormonal therapies. 
  • Tall adult height.

A study from 2015 found that women whose breasts vary in size by 20% or more may be at increased risk for breast cancer. If you have largely uneven breasts your doctor can help you create a breast examination schedule to catch any abnormalities early. 

If you find any of these symptoms in your breasts, schedule a visit with you doctor promptly:

  • A lump in or around your breast.
  • A lump under your arm or in your armpit. 
  • Changes in breast size or shape. 
  • Dimpled or puckered breast skin. 
  • Changes to your nipple. 
  • Red, itchy, or scaly skin on or around your breast. 
  • Discharge coming from your nipple. 
  • Breast or underarm tissue that feels firm and thick. 

Treatment options for breast asymmetry


Unfortunately, surgery is the only treatment option that will leave patients with evenly sized breasts. Doctors can perform many types of plastic surgeries to make breasts look equal in size and normally developed. Oftentimes doctors will only operate on one breast, reducing the invasiveness of this treatment. 

Breast asymmetry surgery is typically performed at plastic surgery clinics. Your health insurance may cover some or all of the procedure if it’s deemed reconstructive. Provincial healthcare coverage may also pay for breast asymmetry surgery if the size difference between your breasts is large enough. 

Padded bras

If you aren’t inclined towards surgery and your breast asymmetry is fairly minor, an adjustable padded bra might be the way to go. Some padded bras have “cookies,” which are removable inserts in the cup area. Adding a cookie to the side where your breast is smaller can give the appearance of even breasts. 

Breast asymmetry is a taboo topic in today’s society, especially since the media projects digitally perfected, unrealistic beauty standards. Womens’ bodies are each unique. Even breasts have their own individuality. The good news is that breast asymmetry is very normal. If your breasts are slightly uneven and you’re in good health, there should be no cause for concern. 

Still, breast asymmetry can be distressing if you feel like the difference is noticeable or that there might be a developing medical issue. If you’d like to speak to a doctor about your breast health, you can connect with one online in minutes. 

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