Why Are My Breasts Uneven?

Just how common is it, and might there ever be cause for concern?

Woman Running
Woman Running. Andrew Burton / Staff / Getty Images

If you've ever worried aloud about your breast size before, you've likely been given the talk about positive body image and self-esteem, and how everyone's breasts are different in size and appearance. You should love your body exactly the way it is, is the common party line. And the people who dispense it are absolutely correct.

Similarly, if you've ever mused over the fact that one breast seems slightly larger or smaller than the other, you've likely been told that asymmetrical breasts are perfectly normal.

And that's true, too.

So Why Are My Breasts Uneven?

All breasts, whether symmetrical or not, fluctuate in size during ovulation and menstruation. Breasts are usually fuller and more sensitive during ovulation, and then shrink back to their normal shapes and sizes during menstruation. It's most likely that the variance in the size of your breasts is due to normal growth variations. 

There are other natural causes that cal also lead to this difference in breast size. For example, hormone changes during puberty can cause one breast to start growing before the other.

When Should I Worry About Uneven Breasts?

Have you been conducting regular breast self-exams? You may find a breast lump that is causing one breast to look larger than the other. These lumps are growths of tissue that develop within your breast. They can be cancerous, but many are simply caused by a variety of benign conditions.

Sometimes, breast lumps are actually cysts, (fluid-filled sacs).

These are also generally noncancerous.

Breast lumps can also be caused by fibrocystic breasts, a condition that causes a woman's breasts to feel lumpy or rope-like, which is more common than you'd think. This condition usually isn't any cause for concern but, if you experience persistent or worsening breast pain, you should talk to your doctor.

Finally, breast lumps can be caused by fibroadenoma, non-cancerous breast tumors that vary in size and shape. These can be surgically removed by a breast surgeon should they fail to shrink over time.

When should you be concerned about breast cancer? If you're breasts have always been uneven, you probably don't have to worry. But if you've noticed a sudden change in the size, shape, and/or appearance of your breasts later in life, it could be a sign of breast cancer.

Is There Anything Else That Affects Breast Size?

Other causes of uneven breasts include:

What Can My Doctor Do To Determine The Cause of my Asymmetry?

If necessary, your doctor may recommend a mammogram, a breast ultrasound, or a breast biopsy. There is no evidence that breast asymmetry is an individual risk factor for breast cancer. However, it is important for women to know what is "normal" for their breast appearance and to report any changes to their doctor.


Uneven breasts: Cosmetic problem or health concern? Mayo Foundation for Medical Education and Research (MFMER).

Continue Reading