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Stacey Feintuch

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9 Reasons You Have Uneven Breasts

It's very common for a woman to have uneven breasts, also called asymmetrical breasts. Find out what causes these breast asymmetries.

Menopause & Aging Well

You may have noticed that you or your daughter or someone you know has one breast that's larger than the other. Uneven breasts are a common concern among women.

It's completely normal for breasts to differ slightly from each other. When you have breast asymmetry, you have a difference in form, position or volume of the breast. More than half of all women are affected by this condition. In fact, one study of 100 women who wanted breast augmentation with implants found that 88 percent had natural asymmetries.

The symmetry of your breasts can be measured with a mammogram. You also might be able to get a SCAN-3D, a special type of three-dimensional laser scanning. (Note that it's not typically offered at most breast imaging centers.)

No one really knows why breasts develop differently from one another. But here are a few possible reasons why you or your daughter might be experiencing breast asymmetry:

  1. Normal growth variations. Most of our body parts, such as our eyebrows or our legs, aren't fully symmetrical. So, your uneven breasts may be attributed to normal anatomic variations.
  2. Hormonal changes. When hormones are changing during puberty, one breast can start to grow before the other, even if they stop growing at the same time.
  3. Traumatic injuries. One report described two cases of breast asymmetry that developed as the result of injuries girls received to their “breast bud” area (when breasts begin to develop starting with just a little swelling under the nipple when a girl begins puberty) during gymnastics when they were ages 10 and 11.
  4. Menstrual cycle. Your breast tissue changes throughout your menstrual cycle. For example, breasts may get bigger due to water retention and additional blood flow. They may feel fuller and more sensitive when you're ovulating. They shrink during menstruation. One study found that breasts have the least amount of asymmetry on the first day of ovulation.
  5. An underlying medical or skeletal condition. A rare condition called juvenile or virginal hypertrophy of the breast is where one breast grows significantly larger than the other. It often leads to physical and psychological problems and is typically treated with surgery.
  6. Fibroids or cysts. You may have a fibrous breast lump, which is a tissue growth that develops within your breast, or a cyst, which is a fluid-filled sac. While tissue lumps can be cancerous, most are noncancerous tumors, called fibroids. Lumps can also be caused by fibrocystic breasts, where your breasts feel lumpy or rope-like, or by fibroadenomas, which are noncancerous breast tissues that vary in size and shape. Any sudden or recent differences in breast sizes due to lumps or underlying breast masses should be evaluated by your health care professional, who may refer you to a specialist.
  7. Scoliosis (curvature of the spine). When you have scoliosis, it can widen one side of the rib cage and create uneven breasts. Uneven breasts in developing girls is a common symptom of scoliosis.
  8. Deformities in the chest wall. Chest wall deformities are structural issues that impact the chest and in turn, the breast size, shape and projection. For example, if you have Poland Syndrome, it can cause underdevelopment of breast tissue and areola (the ring of pigmented skin surrounding a nipple) and rib abnormalities. Funnel chest can cause a depression in the breast bone. And pigeon breast can push the breastbone outward and can cause scoliosis.
  9. Breast cancer marker. Some research suggests that breast asymmetry may be a marker for women who have an increased risk of breast cancer. Typically, breast cancer is only a concern if you've always had even breasts but they've become suddenly become uneven as an adult. Speak to your health care provider if you have sudden changes in the shape, size or appearance of your breasts.

If you or your daughter is bothered by the difference in your breasts, talk to your health care provider. If surgery is recommended, you may want to ask about a breast reduction rather than implants. Studies have shown that women with asymmetry who undergo breast reduction are generally more satisfied than those with implants.

Also, know that most doctors will recommend that a girl wait until her breasts have finished growing before considering plastic surgery.

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