Is It Normal to Have Different-Sized Breasts?

Uneven breasts? Here’s what it means when the twins don’t match.

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Every set of breasts are as unique as the women who carry them—they come in all shapes, sizes, and colors. You may have discovered, though, that there are even minor (or major) differences between the two breasts on your own chest.

“It’s very normal to have breasts of different sizes; it’s called asymmetry,” says Jennifer Wu, MD, an ob-gyn at Lenox Hill Hospital in New York City. Breast asymmetry is defined as a difference in form, position, or volume of the breast, and it affects more than half of all women. In fact, your entire body is technically asymmetrical; one side of your body is completely different than the other (although it’s not usually obvious to the human eye).

“Patients sometimes notice [a breast size difference] and they’re worried by it, but I tell them it’s nothing to worry about and [it’s] very common,” says Dr. Wu. “Most women do have a little bit of difference in size and it can be up to one cup size difference between the breast.”


What Causes Breasts to Be Different Sizes?

Alongside your breasts being perfectly mismatched, they can also fluctuate in size. This usually happens when your body is going through hormonal changes, like during pregnancy or while breastfeeding. “Patients often say, ‘I have one breast that’s really great at breastfeeding,’ and that tends to be the bigger one. This will often even out when they’re finished with breastfeeding,” says Dr. Wu.

Your breasts may change during your menstrual cycle too. They may feel fuller and more sensitive when you’re ovulating, and get bigger from water retention and blood flow. “You may notice a difference in the breast size between the two especially right before your period,” says Dr. Wu.  

Generally, slight differences in a woman’s breast size are not a concern. Some key differences, though, could signal a problem. “Occasionally these [changes] can be due to a secondary reason, maybe a curvature in the spine called scoliosis, or a mass in the breast,” says Dr. Wu. If you notice any new or unfamiliar changes to your breast, it’s always wise to call your doctor. Certain breast changes, like nipple retraction or breast dimpling, may be signs of breast cancer.


What You Can Do About Uneven Breasts

Most women who notice that their breasts are different sizes just buy a bra size that fits the larger breast, says Dr. Wu.

But if your uneven breasts are causing distress or affecting your quality of life, you do have options. “I occasionally have patients who are bothered by the difference in their breast sizes. It’s very noticeable and they decide that they want to even out the size by doing a breast reduction on one side or maybe an implant on the other side.”

Now that you’ve brushed up on your boob knowledge, test your smarts with our breast quiz!