ADVICE: Why is one breast bigger than the other?

'Breast asymmetry is natural, and no two breasts are identical.'

Maja Begovic March 12, 2021

Dear Asking for a Friend,

My left breast is smaller than my right breast by a full cup. And every year around this time, when the summer clothes start coming out, I get that familiar feeling of embarrassment over the obvious unevenness of my chest. Surgery sounds like a pretty drastic option, but is something I am willing to explore. What causes breast asymmetry, and what can I do about it? 

Signed, Uneven

Dear Uneven,

Whether they are a touch uneven or considerably mismatched, breast asymmetry is pretty common. Anatomy, genetics and hormones may play a role in breast shape and size.

“Breast asymmetry is natural, and no two breasts are identical,” reveals Dr. Jacqueline Rose Makerewich, plastic and reconstructive surgeon at the Toronto Cosmetic Surgery Institute. “Every woman has some degree of asymmetry, but the extent of asymmetry varies from person to person, and this is most often related to genetics and normal anatomic variation.”

There is also some evidence that suggests that pregnancy can alter breast shape and size when the body experiences hormonal changes and prepares for breastfeeding. After birth, a nursing baby may favour one breast over the other, which may lead to swelling or stretched breast tissue on one side. Other factors, such as injuries to breasts before they have fully developed, radiation, lumps or abnormal cysts may also contribute to breast asymmetry.

Medical conditions such as atypical ductal hyperplasia, which is characterized by excessive growth in breasts’ milk ducts, may also cause uneven breasts. Breast hypoplasia and in rare cases, juvenile hypertrophy are linked to hormonal changes in puberty and breast asymmetry.

Uneven breasts are usually not problematic, but women whose breast size varies by over 20 per cent may be at an increased risk for breast cancer, according to one study.

If breast asymmetry is impacting your quality of life and self-esteem, try speaking with a therapist. If you continue to struggle with your body image, surgical options are available.

Makerewich says that different surgical techniques can be used to correct various elements of breast asymmetry. The larger breast can be changed to match the smaller breast by way of breast reduction, breast lift, or liposuction. Alternatively, the smaller breast can be altered to match the larger breast using an implant, or fat grafting. Areola repositioning and reshaping, breast tissue redistribution, and special suturing techniques can also be used to reshape a breast to create better symmetry.

“Each woman’s unique anatomy should be considered,” says Makerewich, “including factors such as breast shape, breast volume, breast ptosis or droopiness, or nipple and areola position.

According to research, more than 90 per cent of women who end up having a breast augmentation with implants have natural asymmetries.

But, the results from cosmetic surgery are never typical and vary from patient to patient. Those who are dissatisfied with the outcome end up repeating the procedure and can experience depression, social isolation and engage in self-destructive behaviours, according to research by the American Psychological Association. Patients who are satisfied with surgery experience “improvements in body image and quality of life,” according to the same research.

Before you decide on corrective surgery, do your research and be sure to consult at least two board certified plastic surgeons. According to The Canadian Society of Plastic Surgeons website, there is no foolproof way to guarantee your results, but there are some suggestions that can help you navigate the selection process.


Verify the prospective surgeon’s credentials and training with a provincial college and physicians, including hospital admitting privileges in case of complications, and don’t hesitate to call the hospital to verify that information. Make sure you feel comfortable with the surgeon, and take your time to understand the procedure and its risks. Be thorough when discussing what your expectations and ask how often the surgeon performs the procedure you want.

Be wary of providers who try to pressure you into having surgery or those who offer the procedure at a discounted price. And keep in mind that if you choose to have breast surgery, you may require additional touch ups in the future.


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