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 as puberty as a result of genetics. It can also occur during pregnancy as the breasts gets larger in preparation for breastfeeding. Breasts 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 a hormonal contraceptive), it could also be a sign of breast cancer or lymphoma. Industrial Ventilation Duct
This article describes some of the reasons why your boobs may be uneven and when breast asymmetry may be a cause for concern. It also offers coping tips if uneven breasts are making you feel self-conscious.
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).
Breasts may become uneven during pregnancy. They might grow larger and sometimes be lopsided as the body prepares for lactation (breastfeeding). Hormonal changes play a central role.
During breastfeeding, breasts may not be the same shape or size. This is especially true if your baby favors nursing 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.
Other hormonal changes can spur breast asymmetry, including:
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 to benign (non-cancerous) lumps in the breast that affect its appearance, shape, and proportion.
Hypoplastic breasts are those that are underdeveloped. They may be small, thin, spaced far apart, or uneven. The areola (the area around the nipple) may appear large, too.
The cause of hypoplastic breasts may be congenital or acquired:
Scoliosis is 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.
Treatment depends on the severity of the condition and may involve surgery.
Juvenile hypertrophy is 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.
According to research published in Case Reports in Surgery, juvenile hypertrophy commonly starts during puberty with extreme, unilateral breast growth lasting for six months. This is followed by a longer period of slower but continuous breast growth.
Surgery may be recommended to correct juvenile hypertrophy.
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 during embryogenesis (development of an embryo). While not inherently harmful, the excess tissue may need to be removed with surgery.
Diabetic mastopathy is a rare complication of diabetes that causes the formation of painless, hardened masses in the breasts. The condition is associated with long-term use of insulin.
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.
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 after breast 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.
Uneven breasts usually aren't cause for concern. That said, researchers are finding that uneven breasts may be a risk factor for breast cancer.
A 2015 study published 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.
Breast asymmetry is most common with two types of breast cancer:
Breast asymmetry can also occur with a type of blood cancer called lymphoma. This form of cancer involves the lymphatic 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 breast lymphedema (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, or breast biopsy.
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 requested breast implants. The investigators reported that 91% came in part because of asymmetrical breasts.
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.
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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
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By Tracee Cornforth Tracee Cornforth is a freelance writer who covers menstruation, menstrual disorders, and other women's health issues.
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