The only time when these changes might be concerning is when they happen suddenly for no apparent reason.
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.
Verywell / Lara Antal
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.
During breastfeeding, boobs may not be the same shape or size.
This is especially true if your baby favors nursing on one side.
It takes place if 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.
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.
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.
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.
This is followed by a longer period of slower but continuous breast growth.
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.
The condition is associated with long-term use ofinsulin.
Premenopausal females are most commonly affected.
Does Sleeping on Your Side Cause Uneven Breasts?
There is currently no evidence that this is true.
The only situation where sleep position can affect symmetry is right afterbreast augmentation surgery.
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.
This form of cancer involves thelymphatic system, part of which passes through breast tissues.
They might recommend certain exams, like a mammogram,breast ultrasound, orbreast biopsy.
A Word From Verywell
Breast self-awareness is key.
Most of the time a difference in breast size will be benign and nothing to be concerned about.
It’s important to know and be aware of what your normal body looks and feels like.
If there is a sudden change, you should be evaluated by a healthcare provider.
How Do I Handle This in My Day-to-Day?
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.
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 reasonsgenetics, 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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Kayar R, Cilengiroglu OV.Breast volume asymmetry value, ratio, and cancer risk.Breast Cancer (Auckl).
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