Why Are My Breasts Uneven?

A lot of things come in matched sets, but breasts aren't always one of them. Breast asymmetry is when breasts don't match in size, shape, or position. And it's very common.

It's normal for even fully developed breasts to be of varying sizes. Genetics can influence normal variations in development—like breast shape or size differences, for example. That means that if your mother or grandmother had uneven breasts, you probably will too.

You can notice breast asymmetry as early as puberty. During adolescence, or your teenage years, breasts start to develop. One breast may grow more quickly than the other.

It's not clear why this happens. One explanation is that girls may have more breast tissue cells on one side. The cells may be more sensitive to the hormone estrogen, which causes breast tissue cells to grow.

Usually, the other breast will start to "bud" shortly after. Still, it can take a while for it to catch up and even out.

A 2018 study looked at 300 women who were requesting breast implants. They found that 91% had asymmetrical breasts.

This article goes over the reasons you might have uneven breasts and how to cope with them.

causes of uneven breasts

Verywell / Lara Antal

Medical Conditions Affecting Breast Size

Various conditions can affect the symmetry of your breasts.


Breasts may become uneven during pregnancy. Breasts might grow larger and sometimes lopsided as the body prepares for breastfeeding. Hormone changes also play a role.

During breastfeeding, breasts may not be the same shape or size. This is especially true if your baby favors nursing, or feeding, on one side. As long as your child is getting enough breast milk and growing at a steady rate, you don't need to worry about uneven breasts.

Atypical Ductal Hyperplasia

Atypical ductal hyperplasia (ADH) is a condition that affects your breast tissue cells. It occurs when the milk ducts in your breasts have excessive growth. ADH isn't cancer, but it may increase your risk of getting cancer in the future.

In this condition, more cells line the duct than usual. Some of these cells are irregular in shape and size. ADH can lead to benign (non-cancerous) lumps in the breast that affect its appearance. 

Hypoplastic Breasts

Hypoplastic, or underdeveloped breasts, can be small, thin, spaced far apart, or very uneven. The areola (the area around the nipple) may appear large too.

You usually can't identify a cause for breast hypoplasia. Hormones sometimes play a role. But it can also happen because of an injury or a medical condition.

For example, there's a reported case of a teenage girl who had one breast smaller than the other after normal breast development. In her case, it happened after she had an infection called mononucleosis.

Juvenile Hypertrophy

Juvenile hypertrophy occurs when one breast grows much larger than the other. It's a rare condition and the cause is unknown. Researchers believe it's related to hormone sensitivity or hormone production.

According to research published in 2017, this condition appears during puberty. Two factors contribute to the condition. First, extreme breast growth lasts for six months. That's followed by a longer period of slower but continued breast growth. Surgery can correct juvenile hypertrophy.

When Should I Worry About Uneven Breasts?

Uneven breasts aren't usually something you need to worry over. That said, researchers are finding that uneven breasts may be a risk factor for breast cancer.

A 2015 study in Breast Cancer examined the effects of uneven breasts on breast cancer risk. The study found women whose breasts were 20% different in size had a higher chance of breast cancer.

The role between breast asymmetry and breast cancer risk is still largely misunderstood. We need more research to examine the relationship.

For now, let your doctor know if you see any change in either breast's size, shape, or appearance. They might recommend certain exams, like a mammogram, breast ultrasound, or breast biopsy.


Some studies suggest that uneven breasts might raise the risk of breast cancer. More research is needed to see if this is truly the case. Talk to your doctor if you notice any changes in your breasts.

Daily Life and Coping

Uneven breasts are very common and usually nothing to worry over. Still, at a certain point, it might be hard to hide the difference in breast size. Women have reported a size difference of 30% or more is hard to hide in regular clothes.

If you're concerned or self-conscious about your breasts, you have options:

  • Try seeing a professional bra fitter. They can help you find a bra that fits both sides of your chest and hides any difference.
  • Consider meeting with a counselor or mental health professional. They can give you support and guide you toward learning to accept your body.
  • Join an online support group on body image or breast size to connect with women who deal with the same issues.
  • Talk to your doctor about surgical procedures if your breasts are causing health problems or you can't accept them. Some surgeries can help improve the symmetry of your breasts.


Breast asymmetry, or uneven breasts, can be very common. Breasts can vary in size or shape for several reasons—genetics, pregnancy, breastfeeding, and certain medical conditions.

You may not mind having uneven breasts, or you might feel uncomfortable. If you're embarrassed or self-conscious about your breasts, there are options for you depending on what you prefer.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Winocour S, Lemaine V. Hypoplastic breast anomalies in the female adolescent breastSemin Plast Surg. 2013;27(01):042-048. doi:10.1055/s-0033-1343996

  2. Cruz NI. Breast asymmetry in women requesting plastic surgery of the breastP R Health Sci J. 2018;37(4):230‐238. PMID:30548060

  3. Chen JH, Chan S, Yeh DC, Fwu PT, Lin M, Su MY. Response of bilateral breasts to the endogenous hormonal fluctuation in a menstrual cycle evaluated using 3D MRI. Magn Reson Imaging. 2013;31(4):538-44. doi:10.1016/j.mri.2012.10.022

  4. Kader T, Hill P, Rakha EA, Campbell IG, Gorringe KL. Atypical ductal hyperplasia: update on diagnosis, management, and molecular landscapeBreast Cancer Research. 2018;20(1):39. doi:10.1186/s13058-018-0967-1

  5. Hisham A, Abd Latib M, Basiron N. Juvenile breast hypertrophy: a successful breast reduction of 14.9% body weight without recurrence in a 5-year follow-upCase Rep Surg. 2017;2017:3491012. doi:10.1155/2017/3491012

  6. Kayar R, Çilengiroğlu ÖV. Breast volume asymmetry value, ratio, and cancer riskBreast Cancer (Auckl). 2015;9:87-92. doi:10.4137/BCBCR.S32789

  7. Reilley AF. Breast asymmetry: classification and managementAesthetic Surgery Journal. 2006;26(5):596-600. doi:10.1016/j.asj.2006.07.006

By Tracee Cornforth
Tracee Cornforth is a freelance writer who covers menstruation, menstrual disorders, and other women's health issues.