An Overview of Micromastia and Breast Asymmetry

By Mr Hagen Schumacher / 18 Dec 2017

Cosmetic and plastic surgeon Mr Hagen Schumacher discusses the conditions of micromastia and breast asymmetry, and how they can be treated most effectively

What is micromastia?

More than half the female population has asymmetrical breast development during teenage years,1 and according to a study by the Mayo Clinic, nearly seven out of 10 adult women feel their left and right breasts are not similar in appearance.2 Disparity in breast size is actually quite normal, with a 15-20% difference between breasts considered average.3

However, sometimes instances occur when asymmetry becomes highly developed or the breasts remain extremely small post-puberty. The medical term for the latter is micromastia, which is the post-pubertal underdevelopment of a woman's breast tissue. This is also sometimes referred to as breast hypoplasia.4 Women suffering with this condition fundamentally have two nipples on a flat chest rather than developed mammary glands.

There are two types of micromastia: bilateral and unilateral. Bilateral is when there is no breast tissue on either side of the chest. Unilateral is when there is breast tissue on one side and none, or a significantly smaller amount of tissue, on the other side.

Women often have asymmetrical breasts as a result of micromastia. For example, in a study of 111 patients with micromastia, over 95% exhibited breast asymmetry.5 While these conditions are not uncommon, they can have an enormous impact on a woman's self-esteem and confidence.

What causes micromastia and breast asymmetry?

Some of the causes of micromastia can be related to congenital defects presented at birth, such as abnormalities in the pectoral muscles. They may be evident when a child is born, for example; in the case of Poland syndrome,6 where part of the chest wall muscle is missing, or they may only become apparent in adolescence, for example; mammary hypoplasia or hyperplasia, or breast asymmetries.

Lifestyle factors in later life can sometimes enhance asymmetry of underdeveloped breasts. During pregnancy and breastfeeding, the size and shape of the breasts can change.7 As breast tissue swells with milk, and then shrinks again once breastfeeding has ended, the contours of the bust line may change.

Breast deformities can also be acquired as a result of trauma, burns, tumours, infection or endocrine dysfunction

When it comes to breastfeeding, it doesn’t matter how much a woman tries to feed the baby evenly from both breasts, the child may sometimes prefer one over the other. Ultimately, one of the breasts may stretch and appear uneven as time passes. It is also possible for one breast to return to its pre-pregnancy size while the other stays larger, droops, or flattens more. Some patients may even end up with one breast permanently a full cup size smaller or larger than the other.8

Body alignment can play a role in breast asymmetry. The fat deposits and muscles in the body tend to become more evenly distributed when the body is in perfect alignment. The truth, however, is that during a person’s life, sleeping positions, injuries, stress, and posture, will cause body alignment to change and this over-development of the muscles causes fat tissue in the breasts to appear uneven. Breast deformities can also be acquired as a result of trauma, burns, tumours, infection or endocrine dysfunction.

Treatment of serious cases

The best procedures to remedy severe micromastia usually involve surgery. One of the options available is breast augmentation with implants.

Breast implant surgery can address the problems of both bilateral and unilateral micromastia. For bilateral micromastia, both the implants will be the same size. For unilateral micromastia, implants will be used to help the breasts appear as similar in size as possible. ‘Gummy bear’ high-strength cohesive silicone gel implants, or regular silicone gel implants, create the most natural looking results in women with very little breast tissue, as these implants have a decreased chance of rippling.9

However, if significant asymmetry has occurred as well, a combination of breast reduction, breast uplift and nipple repositioning might also be necessary. Depending on each case, it might mean making the smaller breast bigger, the bigger breast smaller and correcting nipple position and size. There is a tendency for patients to request the smaller breast to be larger, but often the better symmetry is achieved in reducing the larger breast to the smaller breast. Removing excess tissue from the larger breast creates a more natural and long-term result without the need for a surgical implant. Most breast procedures such as this are day cases and may require an overnight stay in hospital after the procedure.

Issues to consider

General issues with breast surgery can involve scarring, possible interference with breastfeeding and sometimes, a risk to the nipple itself in terms of its blood supply. When it comes to obvious asymmetry, there’s a need to thoroughly check a patient’s breasts prior to surgery. This is because some research suggests breast asymmetry may be a sign of an increased risk of breast cancer.10

In order to detect any signs of cancer it would be advisable for the patient to have either an ultrasound or mammogram pre-operation. The purpose of this would be to detect any significant disorder of the breast(s) prior to surgery, so the problem can be resolved beforehand.

With micromastia, there is often a debate as to when, and if, surgical intervention is appropriate for younger patients

The incidences of new breast cancer cases are increasing at a yearly rate.11 It is essential to detect an early cancer so cosmetic procedures do not distort and diminish the opportunity for cure, or limit the usefulness of lumpectomy in cancer treatment. If the patient is between 18 to 40 years’ old, I would recommend they get an ultrasound prior to surgery, whereas if the patient is post 40, a mammogram is highly advised. This is because a patient under 40 is considered low risk and younger patients also have denser breast tissue, making a mammogram difficult to read.12

With micromastia, there is often a debate as to when, and if, surgical intervention is appropriate for younger patients. However, research has demonstrated significant breast asymmetry can cause adolescent girls and young women to score lower on measurements of mental health, than those with a greater degree of breast evenness.13 

Doctors at Boston Children's Hospital assessed 59 girls between the ages of 12 and 21 whose breasts differed by at least one cup size.14 When compared to a control group of girls without breast asymmetry, the patients were found to have lower self-esteem and worse emotional wellbeing than their even-breasted counterparts. One of the study's authors, Dr Brian Labow, suggested early intervention, such as consultation, support and surgery if necessary, can help reduce the mental health effects of these conditions.

However, surgery would probably not be advised if a patient is still going through puberty, as breast asymmetry can even itself out as the body continues to develop.15 There are occasionally cases of self-perceived micromastia, which involves a discrepancy between a person's body image and their internalised images of appropriate or desirable breast size and shape. Patients who demonstrate an obsession with very minor issues could be suffering from mental health conditions such as body dysmorphia disorder (BDD).

Whilst procedures are designed to meet what patients think to be desirable and may, in some cases, alleviate psychological suffering,16 those with more serious mental health conditions may actually worsen, rather than improve, their illness following surgery.

Some energy devices are also used which aim to strengthen, lift and tone the pectoral muscle by emitting microcurrents which causes involuntary contraction

At MyAesthetics, the clinic I am based at, we believe the more scrupulous, face-to-face time we have with the individual, the better. We always offer and encourage patients to have two consultations, prior to surgery with no maximum visits. Whilst many individuals don’t always need or want a second consultation, this does mean they can take as much time as they need to decide whether or not surgery is for them and we have unlimited opportunities to assess their psychological welfare.

If still unsure about a patient’s psychological wellbeing after follow-up consultations, I believe all potential patients should be referred to a psychiatrist for further evaluation. Psychologists report specialist cognitive behavioural therapy (CBT) is most effective for those with BDD.17 CBT is said to work because it focuses on the experience of patients when they are alone, rather than in social situations, and the patient is encouraged to focus on all the characteristics of his or her self to develop a more helpful or flexible view.18

Non-surgical alternatives

If breasts are very underdeveloped or there is a highly obvious asymmetry, it is unlikely this can be corrected without surgery. However, for smaller differences, there are non-surgical treatments that may help. One treatment option that can provide a more natural result is a fat transfer augmentation.19 Instead of putting an implant in the smaller breast, it can be augmented using the patient’s own body fat. This procedure is beneficial as breasts are kept natural-looking and as similar to each other as possible. Some practitioners use PRP for rejuvenation purposes in the breasts and claim they can restore some fullness and sensitivity to them. There is also evidence of benefits to using PRP in conjunction with fat transfer, as it is said to help with resorption.20

Some energy devices are also used which aim to strengthen, lift and tone the pectoral muscle by emitting microcurrents which causes involuntary contraction. However, practitioners often have to repeat this procedure around 12 to 15 times to achieve best results.21

Occasionally, patients ask for fillers to be put into the smaller breast and, although this would be possible, fillers are only designed for small amounts of volume. If used to augment the breast the results would not only be temporary, but also extremely expensive, as treatment would need to be repeated regularly.22 Therefore, I would personally advise against this method.


Any procedure that can make someone feel better about how they present themselves to the world is worth considering. Part of that consideration, however, includes the risk/benefit ratio of the procedure and whether non-surgical options would also be a good alternative. If practitioners who are conducting surgical interventions all provide effective screening, have sufficient psychological education and offer unlimited consultations and extensive face-to-face time, it means patients receive the appropriate support and treatment they need. 

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