Uneven Breasts During Lactation: How Can They Be Corrected?

Uneven breasts during lactation are not considered a medical problem, but the natural effect of interaction with the baby. Rarely is this condition associated with any disease.
Uneven Breasts During Lactation: How Can They Be Corrected?

Written by Edith Sánchez

Last update: 10 August, 2022

It’s very common for a woman to have uneven breasts during breastfeeding. In fact, it’s estimated that up to 85% of women have uneven, or different-sized, breasts without having given birth. And that may become more noticeable when they’re breastfeeding.

Breast unevenness varies from woman to woman. Sometimes it’s very noticeable and other times, the asymmetry is less obvious, to the point that it goes unnoticed.

The truth is that it isn’t a medical condition and shouldn’t cause concern.

It’s worth mentioning that, when a woman feels uncomfortable with uneven breasts, there are also ways to help both breasts acquire a similar size. We’ll talk about this later on in the article.

There are almost always uneven breasts

It is normal for there to be some asymmetry in breasts, as is the case with other parts of the body (arms and legs). It’s normal for there to be a slight difference in shape or length, and this isn’t a problem.

During breastfeeding, it’s normal for the presence of uneven breasts to be more evident. It’s estimated that 1 in 4 mothers have this condition during breastfeeding. One breast looks larger than the other, but everything returns to normal when this stage is over.

However, about 15% of women retain breast unevenness. And it isn’t necessary for them to be breastfeeding for it to be evident. Even though it doesn’t interfere with normal breast function, it can cause discomfort.

A woman holding her breasts.
Uneven breasts are present during and outside of breastfeeding. They do not constitute a health risk.

Why does it happen?

In principle, uneven breasts are due to anatomical factors. The shape of the thorax, the curvature of the ribs, or the position of each shoulder are factors that generate asymmetries in the breasts. It’s also possible for genetics to play a role.

However symmetrical the breasts may be, there tends to be a greater unevenness during breastfeeding. This is because babies tend to prefer one breast over the other. Thus, the baby’s preferred breast tends to increase in size.

The production of breast milk in each breast is regulated by a substance called lactation inhibitory factor (FIL). When the baby takes too much milk from one breast, the FIL responds by encouraging the production of more milk. Thus, one breast is fuller than the other.

The effect of the above is uneven breasts. This will most likely remain the case throughout breastfeeding, because the baby’s preferred breast will have more milk ducts. It’s also possible that the same thing will occur in subsequent pregnancies.

Health effects of uneven breasts

Uneven breasts are hardly ever considered to be a medical problem. The disparity rarely affects the ability to produce milk and breastfeed regularly. Even if one breast doesn’t produce nourishment, the infant can meet its needs with the other breast.

This asymmetry should only be discussed with your health care provider when one breast is visibly smaller than the other from the beginning and doesn’t change in size during pregnancy or after giving birth.

This may be due to a rare condition known as hypoplastic breasts. This occurs when one of the breasts doesn’t have enough glandular tissue and this leads to poor or no milk production.

In other cases, everything returns to normal when breastfeeding ends and the breasts stop producing milk. Thus, the breasts return to the way they were before giving birth.

In most cases, uneven breasts are a temporary condition.

How to correct uneven breasts during breastfeeding

To correct uneven breasts during breastfeeding, it’s best to offer the baby the smaller breast before the other at the start of feeding. This causes that breast to start producing more milk and, consequently, to increase in volume.

If the baby resists or refuses to suckle from a particular breast, you need to find out why. The nipple may have some difficulty, there may be a blockage in the ducts, or the child may have a problem themselves, such as an ear infection.

Another alternative is to use the breast pump to stimulate the smaller breast. This is a way to get the breast to produce more and increase in size. However, the other breast shouldn’t be neglected either, as the asymmetry could be reversed.

Uneven breasts usually correct themselves after breastfeeding ends. A doctor or physiotherapist can give indications for toning and shaping the breasts more attractively when weaning occurs.

Examining a breast.
You can ask for a gynecological consultation if you think your uneven breasts are pathological. It’s very likely that there’s no underlying disease.

If the inequality persists, consult

Uneven breasts are rarely a health problem, although for some women they can become an aesthetic problem. It should be remembered that this is a temporary condition and that it can be corrected with the techniques already mentioned.

However, if, after breastfeeding, the uneven breasts persist and it’s too noticeable or bothersome, the best thing to do is to talk to your doctor. There are types of surgery and other treatment that can be used to modify the asymmetry.

It might interest you...
Breasts Don’t Really Sag from Breastfeeding
Step To Health
Read it in Step To Health
Breasts Don’t Really Sag from Breastfeeding

The available scientific information allows us to affirm that some breasts don't sag from breastfeeding due to changes induced by gestation.



  • Urquizo Aréstegui, R. (2014). Lactancia materna exclusiva: ¿siempre? Revista Peruana de Ginecología y Obstetricia, 60(2), 171-176.
  • Rennison, Michelle E., et al. “Inhibition of constitutive protein secretion from lactating mouse mammary epithelial cells by FIL (feedback inhibitor of lactation), a secreted milk protein.” Journal of Cell Science 106.2 (1993): 641-648.
  • Matthes, A. D. C. S., & Sgrignoli, R. B. (2009). Definición de senos normales para mujeres en Menacme. Revista Latino-Americana de Enfermagem, 17, 108-112.
  • Téllez-Olvera, Alejandro, Jorge Romero-Álvarez, and Miguel Ángel Salgado-Molina. “Poland’s syndrome. Case report.” Revista Médica del Instituto Mexicano del Seguro Social 48.1 (2010): 79-82.