What It Means When Your Left Breast Is Bigger Than Your Right

Photo Credits: Sam Edwards/ Getty Images | Image Used for Illustrative Purposes Only

I've heard people say that it's a common thing for a woman's left breast to be bigger than her right, but I wasn't sure if it was true or what the science was behind it. However, when I'd ask my friends about it, they mostly agreed it was also true for them. So why is this the case and what does it mean? Here's the inside scoop.

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“The majority of women have asymmetrical breasts—some women realize it, but many do not,” says Concord, CA plastic surgeon Eric Mariotti, MD. “One study found that 91 percent of women have some asymmetry, whether it is regarding volume, the height of the nipples, or the chest wall. Most of the time these differences are very subtle, but other times they can be quite obvious. As a plastic surgeon who specializes in breast surgery, it is part of my job to educate women about them either way.”

Dr. Jessica A. Shepherd, director of Minimally Invasive Gynecology at the University of Illinois at Chicago says the most common reason for asymmetry is hormonal changes. "Breast asymmetry is typically seen in puberty where there are rapid growth spurts, and it is possible that one breast responds more to surging estrogen levels than the other." Dr. Mariotti agrees. “One breast may have a different percentage of true breast tissue versus fatty tissue, and may therefore react to hormonal changes differently,” he says. “Genetics also play a big role: If a woman’s mother or grandmother had asymmetrical breasts, the chances are higher that she may have asymmetry as well.”

In addition to hormonal changes during puberty, the body’s physical development can also affect the appearance of the breasts. “Any bit of scoliosis in the spine can not only make the breasts appear uneven, but if the scoliosis appears during puberty, the development of the breasts can also be different,” says Pasadena, CA plastic surgeon Lily Lee, MD. “Similarly, the shape of a person’s rib cage might not be the same from right to left. Even if a person’s breasts are exactly the same size and shape, if the foundation that they sit on (rib cage) is uneven, the breasts will appear uneven.” Houston plastic surgeon Henry Mentz, MD says a woman’s athleticism can influence the share of her rib cage as well. For those who are very athletic, “the left rib cage may be slightly higher than the right because the heart and surrounding muscles have lifted the rib cage slightly. Many people have this condition,” he says. “Some patients who are right-handed or left-handed may also have a difference in the fullness of their muscle on the corresponding side, especially if they play sports where they predominantly use one hand, such as tennis.”

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Grand Rapids, MI, plastic surgeon Bradley Bengtson, MD sums it up plain and simple: "One of my favorite professors used to tell me, 'Breasts are sisters, not twins,' and I tell my patients that too."

There haven’t been many legit studies on breast size, but Dr. Shepherd finds a couple especially interesting: "One study in particular was done with 100 women who desired breast augmentation, and of those women, 88 percent had natural asymmetries. Also seen in a study published in the Annals of Plastic Surgery, 600 women were evaluated, and it was found that the left breast was larger." 

So, if your left breast is larger than your right, no need to fret. It appears to be one of those unexplainable anatomical mysteries that affects many women of all different shapes and sizes for no good reason. But, if your asymmetry is significant and it bothers you, there are several ways it can be corrected.

FAT TRANSFER
"For mild asymmetry, we use fat transfer because we can shape the smaller breast and add small increments of volume where we want it," says Dr. Bengtson. Fat transfer involves removing fat from one area of the body that has excess (typically the abdomen or thighs), cleaning it up and then injecting it into volume-deficient areas. Many doctors prefer using fat over other options because it’s from the patient’s own body, has a natural look and feel, and typically comes with a lower risk of complications.

BREAST IMPLANTS
If the symmetry is more significant, a breast implant can be used to create balance. "Implants are usually 30–40 cc different in volume for the next implant size up or down so we can definitely dial in and make breasts more symmetrical. In addition, we have four different projections of implants, so in patients with rib and chest wall deformities (which is extremely common), we can alter projection of the implant and thus the breast as well," explains Dr. Bengtson. Adds Dr. Lee, “We now have such a range in sizes and shapes of breast implants that we can get asymmetries closer than ever before.”

Dr. Mariotti adds that because no two cases are identical, “these types of procedures take a surgeon with lots of experience with breast surgery to get right.” It’s important to find a board-certified plastic surgeon who is qualified and can show you before-and-after images of other patients.

A high-tech benefit for patients interested in correcting asymmetries with implants is the Vectra 3-D imaging system. “Vectra takes several 3-D photographs with a special camera and analyzes them in the computer to show differences in size and shape of the breasts and provide guidance in breast augmentation regarding the size, shape and placement of the implants,” Dr. Mentz explains. “It’s very useful and precise, and it’s illuminating for patients to see themselves with accurate measurements and views from above, below and to the side. It also allows them to see themselves with a bathing suit top on or without to see if the implant size suits them.”

BREAST LIFT
A surgical lift can be done without inserting a breast implant in many cases, especially if it’s to correct uneven nipples. “Sometimes one nipple may be lifted more than the other, and when the nipple position is more than 20 millimeters higher than the other side, a breast lift can help even things out,” explains Dr. Mentz. If it’s the nipples themselves that are different sizes, they can be surgically altered to match as well.

Because breast asymmetries are so common, it's important to be aware of what is a "normal change" in your breast size and what isn't. Recognizing signs of breast cancer, which will affect one in nine women in their lifetime, is crucial for women. "Be sure to talk to your doctor if you have changes in how your breasts look or feel, such as a lump or firm feeling that is near your breast or under your arm," says Dr. Shepherd. "Also check for nipple discharge or changes that do not look like milk and are possibly bloody. Another sign could be skin on your breasts that is itchy, red, scaling, dimpled or puckered."