Unequal breast size

  • It is quite common for one breast to be bigger than the other as development occurs during puberty. Usually the breasts become the same size over time and do not need any treatment. However, if the breasts have not become more or less an equal size by the age of about 16 years old (or near the end of puberty), they will probably remain unequal. About one in four adult women have some degree of asymmetry of the breasts.

    In some adolescents the problem is that one breast is overdeveloped, whereas in others the smaller breast is underdeveloped.

    When to see a doctor

    There is no need to see a doctor for unequal breast size during puberty (when the breasts are still developing). However, you may wish to see a GP for advice if the breasts are of unequal size at the end of puberty. You may be referred to an endocrinologist (doctor specialising in conditions related to hormones).

    Treatment for unequal breast size

    There is no medical need for treatment for uneven breast size.

    The difference in breast size is usually caused by the fat layers, not the ducts that produce milk. Therefore, a mother with unequal breast size should be able to breastfeed as usual from both breasts. The amounts of milk produced should be the same from each breast. 

    Because the difference in breast size is usually due to the fat layers, uneven breast size has no effect on the risk of breast cancer. If you have any concerns, you should discuss this with your doctor.

    There are three treatment options for uneven breast sizes that can improve the cosmetic appearance of the breasts:

    External breast prosthesis

    An external breast prothesis is worn with a special bra. The prothesis has a hollow on the inside where the smaller breast fits comfortably. They are filled with a skin-coloured gel and feel just like a breast. The prosthesis can be matched to the size and shape of the other breast. 

    The prosthesis can be held in place with tape that can be left on the skin for several days at a time. Some breast prostheses can be inserted into special pockets in swimsuits or active wear.

    There is no health risk associated with the breast prosthesis as it is worn outside the body. 

    Breast reduction

    Surgery to reduce breast size is done as an operation under general anaesthetic (where you are put to sleep) by a plastic surgeon.

    Breast reduction can affect milk production if breast tissue is removed. Nipple placement is also important to ensure future breast feeding goes well. Discuss all risks and benefits carefully with a plastic surgeon.

    Breast implant

    Breast implants are done as an operation under general anaesthetic by a plastic surgeon. Implants are now filled with saline (salt water), which is considered harmless to the body. Silicone implants are no longer used because of fears that small amounts of silicone could leak and damage the immune system. Breast enhancement should not cause any problems with breast feeding. Discuss all risks and benefits carefully with a plastic surgeon.

    Key points to remember

    • It is quite common for breast size to be unequal during puberty. If they are different sizes near the end of puberty, they are likely to stay unequal. 
    • There is no medical need for treatment for unequal breast size. Unequal breasts won't affect breastfeeding or increase breast cancer risk.
    • An external breast prothesis looks and feels realistic and has no associated health risks.
    • A breast reduction or breast implant are plastic surgery options that can improve cosmetic appearance. 

    For more information

    • See your GP, paediatrician  or endocrinologist.
    • Talk to a plastic surgeon to discuss treatment options.

    Common questions our doctors are asked

    Which is the safest option: breast reduction or breast implant?

    This is something that should be discussed at length with your plastic surgeon. It will depend on the shape and size of each breast, as well as your desired outcome.

    I have read that unequal breast size is linked with increased risk breast cancer. Is this true?

    This is not true. The asymmetry is usually caused by differences in the fat layers, not the breast tissue. It is important to perform regular self-checks for breast changes, as part of a healthy lifestyle. You can discuss and learn these self-checks with your GP or paediatrician.

    My baby has developed breast tissue, which is uneven, what should I do?

    There are many hormone changes that occur to young babies, especially those who are breastfed. May babies will develop small amounts of breast tissue, and some may even start to make breastmilk! If this is happening with your baby, there is often no cause for concern, but have them seen by your GP or paediatrician.

    Developed by The Royal Children's Hospital Endocrinology and Plastic and Maxillofacial Surgery departments. We acknowledge the input of RCH consumers and carers.

    Reviewed June 2018.

    This information is awaiting routine review. Please always seek the most recent advice from a registered and practising clinician.

    Kids Health Info is supported by The Royal Children’s Hospital Foundation. To donate, visit www.rchfoundation.org.au.


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