Kids Health Info

Unequal breast size

  • It is quite common for a girl to have one breast bigger than the other when she is going through puberty.  Usually they 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 time a girl is about 16 years old or near the end of puberty, they will probably remain unequal.

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

    Treatment options

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

    The difference in breast size is usually due to the fat layers, not the milk producing ducts. Therefore women with unequal breast size should be able to breast feed as usual from both breasts. The amounts of milk produced should be the same. 

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

    These are three treatment and plastic surgery options for uneven breast sizes for women who wish to improve the cosmetic appearance of their breasts:

    External breast prosthesis

    These are worn inside a special bra next to the skin. They have a hollow on the inside where the smaller breast fits inside very comfortably. They are filled with a skin colored gel and feel just like a breast. They can be easily matched to the size and shape of the other breast. The nipple can also be matched to the other breast. The quality is so good that it will look completely normal even under a tight t-shirt. It can be held in place with tape that can be left on the skin for several days at a time. More simple padding can be also worn with swimsuits.

    There is no risk to health from the implants as they are worn outside the body. You need to buy the prosthesis but can claim a lot of the cost back from some health funds. Check with your insurance company. 

    You may also be able to claim a tax deduction as a legitimate health expense.

    Breast reduction

    Surgery to reduce breast size is done as an operation under general anaesthetic by a plastic surgeon.

    Breast reduction can affect lactation (milk production) if breast tissue is removed. But it may just mean the baby needs to have more frequent feeds for a longer time. Nipple placement is important to ensure future feeding. 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 being used now are 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.

    For more information

    • Talk to your family doctor or paediatrician 
    • Talk to an Endocrinologist
      If you wish to discuss unequal breast size.
    • Talk to a Plastic Surgeon
      If you wish to discuss treatment options.
    • Factsheets on breast implants: Upfront About Breast Forms booklet  (Please note this is a website primarily aimed at women with breast cancer. The implant information remains the same).

    Produced by the RCH Dept of Endocrinology in consultation with the Dept of Plastic Surgery.  First published Sept 2006.  Updated November 2010.

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This information is intended to support, not replace, discussion with your doctor or healthcare professionals. The authors of these consumer health information handouts have made a considerable effort to ensure the information is accurate, up to date and easy to understand. The Royal Children's Hospital, Melbourne accepts no responsibility for any inaccuracies, information perceived as misleading, or the success of any treatment regimen detailed in these handouts. Information contained in the handouts is updated regularly and therefore you should always check you are referring to the most recent version of the handout. The onus is on you, the user, to ensure that you have downloaded the most up-to-date version of a consumer health information handout.