When one breast produces significantly less milk than the other, this is known as unilateral low supply. This is a common concern for many parents, yet it rarely prevents a successful breastfeeding experience. Milk production operates on a supply-and-demand basis in each breast independently, meaning differences in stimulation or anatomy can lead to noticeable output variations. Understanding the causes and how to address them helps manage expectations and support the feeding relationship.
Understanding Normal Breast Asymmetry
It is common for breasts to be asymmetrical in both size and function, even outside of breastfeeding. This natural variation extends to internal structures, where one breast may have a greater density of milk-making glandular tissue than the other. A production split of 60% from one breast and 40% from the other is typical, and some experience a difference as high as 70% to 30%.
The difference is usually not a cause for concern, as the higher-producing breast often compensates for the other. Asymmetry can develop over time due to the baby’s preference for one side, leading to more frequent milk removal from that favored breast. When one side is drained more consistently, the body signals that breast to increase production, while the less-stimulated side naturally lowers its output.
Specific Causes of Unilateral Low Supply
While minor differences are normal, a drastic reduction in one breast’s output often points to a specific physical or mechanical cause. A history of breast surgery, such as reduction mammoplasty, augmentation, or certain biopsies, can damage the delicate milk ducts and nerves required for milk production and the let-down reflex. Scar tissue from these procedures can physically impede the flow of milk from the glandular tissue to the nipple.
Unresolved infection or trauma can also create a significant supply imbalance. A severe case of mastitis or a breast abscess can cause permanent damage to the milk-producing cells (alveoli) within that specific breast. The resulting tissue damage can limit the breast’s ability to respond to the prolactin hormone necessary for milk synthesis.
Mechanical issues related to feeding are among the most common causes of unilateral low supply. If the baby has a persistent poor latch or positioning only on one side, that breast will not be effectively drained, signaling the body to decrease supply. The baby may also develop a preference for one side due to a faster or slower milk flow, or physical discomfort in a certain position, leading to less stimulation of the non-preferred breast.
Focused Strategies to Boost Production
Boosting the supply on the lower-producing side involves increasing the demand signal to that specific breast. Always offer the baby the lower-supply breast first at the start of every feeding session. Babies are hungriest and suckle most vigorously at the beginning of a feed, providing maximum stimulation to the underperforming side.
Focused pumping can stimulate milk production on the desired side, especially after the baby has finished nursing. Power pumping mimics cluster feeding: pump on the low-supply side for 10 to 20 minutes, rest for 10 minutes, and repeat this cycle for an hour once a day. Using breast compression while nursing or pumping can also improve milk drainage and increase the volume removed from the breast.
Ensure the baby is positioned comfortably and latching deeply on the lower-producing side to facilitate effective milk transfer. Trying different nursing positions may help the baby drain the breast more efficiently if a specific hold causes discomfort or an ineffective latch. Consistency in applying these targeted techniques is key, as it may take several days to a week to see a measurable increase in output.
When Professional Medical Advice is Necessary
While most cases of unilateral low supply are manageable, certain signs warrant consultation with a healthcare provider or an International Board Certified Lactation Consultant (IBCLC). If the production disparity is severe and the baby shows signs of failure to thrive, such as poor weight gain or insufficient wet diapers, professional help is needed to ensure adequate nutrition. An IBCLC can assess the baby’s latch and sucking mechanics to identify underlying issues.
Physical changes in the breast should be evaluated promptly by a medical professional. This includes the sudden appearance of a new lump or mass that does not resolve after feeding or pumping. Other concerning signs are fever, severe pain, or flu-like symptoms, which indicate an infection like mastitis that needs medical treatment. Changes in the skin texture of the breast, such as dimpling resembling an orange peel (peau d’orange), should be immediately assessed to rule out serious conditions.