Table of ContentsView AllTable of ContentsMedical ConditionsWhen Should I Worry?How Do I Handle This in My Day-to-Day?
Table of ContentsView All
View All
Table of Contents
Medical Conditions
When Should I Worry?
How Do I Handle This in My Day-to-Day?
It’s normal for breasts to be a little uneven, and, in most cases, having one boob bigger than the other is not a problem. Breast asymmetry can start as early aspubertyas a result of genetics.It can also occur during pregnancy as the breasts get larger in preparation for breastfeeding.Boobs can also get bigger during menopause—and not always evenly.
The only time when these changes might be concerning is when they happen suddenly for no apparent reason. While it may be due to a benign cause (like starting ahormonal contraceptive), it could also be a sign ofbreast cancerorlymphoma.
Verywell / Lara Antal
What Conditions Affect Breast Size?
Breast asymmetry is defined as a unilateral (one-sided) unevenness of breast volume, dimension, and/or position. The cause may be congenital (something you are born with) or acquired (something that you get later in life). Some causes are permanent and others are transient (temporary).
Pregnancy, Breastfeeding, and Other Hormonal Changes
Breasts may become uneven duringpregnancy. They might grow larger and sometimes be lopsided as the body prepares forlactation(breastfeeding). Hormonal changes play a central role.
Other hormonal changes can spur breast asymmetry, including:
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 experience 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 tobenign(non-cancerous) lumps in the breast that affect its appearance, shape, and proportion.
Hypoplastic Breasts
Hypoplasticbreasts are those that are underdeveloped. They may be small, thin, spaced far apart, or uneven. Theareola(the area around the nipple) may appear large, too.
The cause of hypoplastic breasts may be congenital or acquired:
Scoliosis
Scoliosisis the abnormal curvature of the spine. Breast asymmetry is common with this congenital disorder, mainly in relation to the position of each breast.
Scoliosis is usually recognized in childhood or adolescence and may be subtle or severe. Different types of curvature can occur with scoliosis, which can lead to uneven shoulders, arms, or hips. There may be a tilt to one side of the body, causing one breast to be lower than the other.
Scoliosis treatmentdepends on the severity of the condition and may involve surgery.
Juvenile Hypertrophy
Juvenile hypertrophyis a benign condition in which one breast grows much larger than the other. It’s a rare congenital disorder, the cause of which is unknown.
Cosmetic surgery may be recommended to correct juvenile hypertrophy, but it’s usually done later in life, long after the breasts are done forming.
Ectopic Breasts
Ectopic breast tissue (EBT) is a rare condition affecting up to 6% of the population in which breast tissues are located somewhere other than where they are supposed to be. EBT is most common in Asian people in whom breast tissues can form anywhere along the milk line running from the armpit to the groin.
Masses of tissue can sometimes appear in the abdomen as tumor-like lumps. Others develop near normal breast tissues, affecting the size and shape of the breast.
EBT is thought to start duringembryogenesis(development of an embryo). While not inherently harmful, the excess tissue may need to be removed with surgery.
Diabetic Mastopathy
Diabetic mastopathy is a rare complication ofdiabetesthat causes the formation of painless, hardened masses in the breasts. The condition is associated with long-term use ofinsulin.
For reasons unknown, insulin exposure can cause the development of fibrous tissue masses in the breasts that are easily mistaken for breast cancer. Premenopausal females are most commonly affected.
The growth can make one breast look larger than the other and many even cause the breast position to shift.
Does Sleeping on Your Side Cause Uneven Breasts?For generations, people with breasts have been told that sleeping on their side is going to make their boobs uneven. There is currently no evidence that this is true.The only situation where sleep position can affect symmetry is right afterbreast augmentation surgery. The proper sleep position—on your back with your upper body slightly elevated—is needed to take pressure off the implants and ensure everything heals in the correct position.
Does Sleeping on Your Side Cause Uneven Breasts?
For generations, people with breasts have been told that sleeping on their side is going to make their boobs uneven. There is currently no evidence that this is true.The only situation where sleep position can affect symmetry is right afterbreast augmentation surgery. The proper sleep position—on your back with your upper body slightly elevated—is needed to take pressure off the implants and ensure everything heals in the correct position.
For generations, people with breasts have been told that sleeping on their side is going to make their boobs uneven. There is currently no evidence that this is true.
The only situation where sleep position can affect symmetry is right afterbreast augmentation surgery. The proper sleep position—on your back with your upper body slightly elevated—is needed to take pressure off the implants and ensure everything heals in the correct position.
When Should I Worry About Uneven Boobs?
One boob that is larger than the other usually isn’t a cause for concern. That said, researchers are finding that uneven breasts may be a risk factor for breast cancer.
A 2015 study published inBreast Cancerexamined 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.
Breast asymmetry is most common with two types of breast cancer:
Breast asymmetry can also occur with a type of blood cancer calledlymphoma. This form of cancer involves thelymphatic system, part of which passes through breast tissues.
Research suggests that around 20% of people with lymphoma develop notable changes in breast symmetry, while 8% experience tissue hardening and breastlymphedema(the build-up of fluid where the lymph system is damaged or blocked).
Let your healthcare provider know if you see any change in either breast’s size, shape, or appearance. They might recommend certain exams, like a mammogram,breast ultrasound, orbreast biopsy.
A Word From Verywell
—CORDELIA NWANKWO, MD, MEDICAL EXPERT BOARD
Uneven breasts are very common and usually nothing to worry about. Still, at a certain point, it might be hard to hide the difference in breast size.
If you’re concerned or self-conscious about your breasts, you have options:
A 2018 study interviewed 300 cisgender women who requestedbreast implants. The investigators reported that 91% came in part because of asymmetrical breasts.
Summary
Breast asymmetry, or “uneven boobs,” 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 resolution with various approaches.
14 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Lim LY, Ho PJ, Liu J, Chay WY, Tan MH, Hartman M, et al.Determinants of breast size in Asian women.Sci Rep. 2018 Jan 19;8(1):1201. doi:10.1038/s41598-018-19437-4.Winocour S, Lemaine V.Hypoplastic breast anomalies in the female adolescent breast.Semin Plast Surg. 2013;27(01):042-048. doi:10.1055/s-0033-1343996Hudson SM, Wilkinson LS, Denholm R, De Stavola BL, do-Santos-Silva I.Ethnic and age differences in right-left breast asymmetry in a large population-based screening population.Br J Radiol.2020 Jan;93(1105):20190328. doi:10.1259/bjr.20190328Chen 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.2012.10.022Kader T, Hill P, Rakha EA, Campbell IG, Gorringe KL.Atypical ductal hyperplasia: update on diagnosis, management, and molecular landscape.Breast Cancer Res. 2018;20(1):39. doi:10.1186/s13058-018-0967-1Winocour S, Lemaine V.Hypoplastic breast anomalies in the female adolescent breast.Semin Plast Surg.2013 Feb;27(1):42–48. doi:10.1055/s-0033-1343996Atici Y, Polat B, Erdogan S, Gürpınar T, Demiröz S.Can breast asymmetry following the treatment of juvenile idiopathic scoliosis with growing rod be prevented? A preliminary analysis.J Korean Neurosurg Soc. 2020 Mar;63(2):228-236. doi:10.3340/jkns.2019.0192Hisham 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-up.Case Rep Surg. 2017;2017:3491012. doi:10.1155/2017/3491012Teixeira IP, Azzopardi C, Chowdhury R, Zsolt O, Castro M, Teh J.Ectopic breast tissue presenting as an enlarging abdominal mass.Radiol Case Rep.2020 Jun;15(6):733–740. doi:10.1016/j.radcr.2020.02.028Guzik P, Geca T, Topolewski P, et al.Diabetic mastopathy. review of diagnostic methods and therapeutic options.Int J Environ Res Public Health.2022 Jan;19(1):448. doi:10.3390/ijerph19010448American Society of Plastic Surgeons.Breast augmentation.Kayar R, Çilengiroğlu ÖV.Breast volume asymmetry value, ratio, and cancer risk.Breast Cancer (Auckl). 2015;9:87-92. doi:10.4137/BCBCR.S32789Raj SD, Shurafa M, Shah Z, Raj KM, Fishman MDC, Dialani VM.Primary and secondary breast lymphoma: clinical, pathologic, and multimodality imaging review.Radiographics. 2019 May-Jun;39(3):610-625. doi:10.1148/rg.2019180097Cruz NI.Breast asymmetry in women requesting plastic surgery of the breast.P R Health Sci J. 2018;37(4):230‐238. PMID:30548060
14 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Lim LY, Ho PJ, Liu J, Chay WY, Tan MH, Hartman M, et al.Determinants of breast size in Asian women.Sci Rep. 2018 Jan 19;8(1):1201. doi:10.1038/s41598-018-19437-4.Winocour S, Lemaine V.Hypoplastic breast anomalies in the female adolescent breast.Semin Plast Surg. 2013;27(01):042-048. doi:10.1055/s-0033-1343996Hudson SM, Wilkinson LS, Denholm R, De Stavola BL, do-Santos-Silva I.Ethnic and age differences in right-left breast asymmetry in a large population-based screening population.Br J Radiol.2020 Jan;93(1105):20190328. doi:10.1259/bjr.20190328Chen 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.2012.10.022Kader T, Hill P, Rakha EA, Campbell IG, Gorringe KL.Atypical ductal hyperplasia: update on diagnosis, management, and molecular landscape.Breast Cancer Res. 2018;20(1):39. doi:10.1186/s13058-018-0967-1Winocour S, Lemaine V.Hypoplastic breast anomalies in the female adolescent breast.Semin Plast Surg.2013 Feb;27(1):42–48. doi:10.1055/s-0033-1343996Atici Y, Polat B, Erdogan S, Gürpınar T, Demiröz S.Can breast asymmetry following the treatment of juvenile idiopathic scoliosis with growing rod be prevented? A preliminary analysis.J Korean Neurosurg Soc. 2020 Mar;63(2):228-236. doi:10.3340/jkns.2019.0192Hisham 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-up.Case Rep Surg. 2017;2017:3491012. doi:10.1155/2017/3491012Teixeira IP, Azzopardi C, Chowdhury R, Zsolt O, Castro M, Teh J.Ectopic breast tissue presenting as an enlarging abdominal mass.Radiol Case Rep.2020 Jun;15(6):733–740. doi:10.1016/j.radcr.2020.02.028Guzik P, Geca T, Topolewski P, et al.Diabetic mastopathy. review of diagnostic methods and therapeutic options.Int J Environ Res Public Health.2022 Jan;19(1):448. doi:10.3390/ijerph19010448American Society of Plastic Surgeons.Breast augmentation.Kayar R, Çilengiroğlu ÖV.Breast volume asymmetry value, ratio, and cancer risk.Breast Cancer (Auckl). 2015;9:87-92. doi:10.4137/BCBCR.S32789Raj SD, Shurafa M, Shah Z, Raj KM, Fishman MDC, Dialani VM.Primary and secondary breast lymphoma: clinical, pathologic, and multimodality imaging review.Radiographics. 2019 May-Jun;39(3):610-625. doi:10.1148/rg.2019180097Cruz NI.Breast asymmetry in women requesting plastic surgery of the breast.P R Health Sci J. 2018;37(4):230‐238. PMID:30548060
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Lim LY, Ho PJ, Liu J, Chay WY, Tan MH, Hartman M, et al.Determinants of breast size in Asian women.Sci Rep. 2018 Jan 19;8(1):1201. doi:10.1038/s41598-018-19437-4.Winocour S, Lemaine V.Hypoplastic breast anomalies in the female adolescent breast.Semin Plast Surg. 2013;27(01):042-048. doi:10.1055/s-0033-1343996Hudson SM, Wilkinson LS, Denholm R, De Stavola BL, do-Santos-Silva I.Ethnic and age differences in right-left breast asymmetry in a large population-based screening population.Br J Radiol.2020 Jan;93(1105):20190328. doi:10.1259/bjr.20190328Chen 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.2012.10.022Kader T, Hill P, Rakha EA, Campbell IG, Gorringe KL.Atypical ductal hyperplasia: update on diagnosis, management, and molecular landscape.Breast Cancer Res. 2018;20(1):39. doi:10.1186/s13058-018-0967-1Winocour S, Lemaine V.Hypoplastic breast anomalies in the female adolescent breast.Semin Plast Surg.2013 Feb;27(1):42–48. doi:10.1055/s-0033-1343996Atici Y, Polat B, Erdogan S, Gürpınar T, Demiröz S.Can breast asymmetry following the treatment of juvenile idiopathic scoliosis with growing rod be prevented? A preliminary analysis.J Korean Neurosurg Soc. 2020 Mar;63(2):228-236. doi:10.3340/jkns.2019.0192Hisham 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-up.Case Rep Surg. 2017;2017:3491012. doi:10.1155/2017/3491012Teixeira IP, Azzopardi C, Chowdhury R, Zsolt O, Castro M, Teh J.Ectopic breast tissue presenting as an enlarging abdominal mass.Radiol Case Rep.2020 Jun;15(6):733–740. doi:10.1016/j.radcr.2020.02.028Guzik P, Geca T, Topolewski P, et al.Diabetic mastopathy. review of diagnostic methods and therapeutic options.Int J Environ Res Public Health.2022 Jan;19(1):448. doi:10.3390/ijerph19010448American Society of Plastic Surgeons.Breast augmentation.Kayar R, Çilengiroğlu ÖV.Breast volume asymmetry value, ratio, and cancer risk.Breast Cancer (Auckl). 2015;9:87-92. doi:10.4137/BCBCR.S32789Raj SD, Shurafa M, Shah Z, Raj KM, Fishman MDC, Dialani VM.Primary and secondary breast lymphoma: clinical, pathologic, and multimodality imaging review.Radiographics. 2019 May-Jun;39(3):610-625. doi:10.1148/rg.2019180097Cruz NI.Breast asymmetry in women requesting plastic surgery of the breast.P R Health Sci J. 2018;37(4):230‐238. PMID:30548060
Lim LY, Ho PJ, Liu J, Chay WY, Tan MH, Hartman M, et al.Determinants of breast size in Asian women.Sci Rep. 2018 Jan 19;8(1):1201. doi:10.1038/s41598-018-19437-4.
Winocour S, Lemaine V.Hypoplastic breast anomalies in the female adolescent breast.Semin Plast Surg. 2013;27(01):042-048. doi:10.1055/s-0033-1343996
Hudson SM, Wilkinson LS, Denholm R, De Stavola BL, do-Santos-Silva I.Ethnic and age differences in right-left breast asymmetry in a large population-based screening population.Br J Radiol.2020 Jan;93(1105):20190328. doi:10.1259/bjr.20190328
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
Kader T, Hill P, Rakha EA, Campbell IG, Gorringe KL.Atypical ductal hyperplasia: update on diagnosis, management, and molecular landscape.Breast Cancer Res. 2018;20(1):39. doi:10.1186/s13058-018-0967-1
Winocour S, Lemaine V.Hypoplastic breast anomalies in the female adolescent breast.Semin Plast Surg.2013 Feb;27(1):42–48. doi:10.1055/s-0033-1343996
Atici Y, Polat B, Erdogan S, Gürpınar T, Demiröz S.Can breast asymmetry following the treatment of juvenile idiopathic scoliosis with growing rod be prevented? A preliminary analysis.J Korean Neurosurg Soc. 2020 Mar;63(2):228-236. doi:10.3340/jkns.2019.0192
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-up.Case Rep Surg. 2017;2017:3491012. doi:10.1155/2017/3491012
Teixeira IP, Azzopardi C, Chowdhury R, Zsolt O, Castro M, Teh J.Ectopic breast tissue presenting as an enlarging abdominal mass.Radiol Case Rep.2020 Jun;15(6):733–740. doi:10.1016/j.radcr.2020.02.028
Guzik P, Geca T, Topolewski P, et al.Diabetic mastopathy. review of diagnostic methods and therapeutic options.Int J Environ Res Public Health.2022 Jan;19(1):448. doi:10.3390/ijerph19010448
American Society of Plastic Surgeons.Breast augmentation.
Kayar R, Çilengiroğlu ÖV.Breast volume asymmetry value, ratio, and cancer risk.Breast Cancer (Auckl). 2015;9:87-92. doi:10.4137/BCBCR.S32789
Raj SD, Shurafa M, Shah Z, Raj KM, Fishman MDC, Dialani VM.Primary and secondary breast lymphoma: clinical, pathologic, and multimodality imaging review.Radiographics. 2019 May-Jun;39(3):610-625. doi:10.1148/rg.2019180097
Cruz NI.Breast asymmetry in women requesting plastic surgery of the breast.P R Health Sci J. 2018;37(4):230‐238. PMID:30548060
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