A drop in milk supply can be unsettling for a parent. Milk volume is managed by a complex interplay of hormonal signals and the mechanics of milk removal, meaning a decrease is often a direct response to a change in the body or the feeding routine. Understanding the specific cause of a supply drop is the first step toward correcting the issue and returning to an adequate milk volume.
Issues with Milk Removal and Feeding Schedule
The body operates on a simple supply-and-demand system, where the rate of milk production is directly linked to how frequently and completely milk is removed from the breast. When milk is not adequately removed, a protein known as Feedback Inhibitor of Lactation (FIL) accumulates, sending a signal to the mammary cells to slow down production. This is the most common reason for a supply dip, and it often stems from a change in feeding management.
Infrequent milk removal, whether due to a baby suddenly sleeping for longer stretches or a parent scheduling feeds rather than following hunger cues, is a frequent trigger for decreased supply. The breast needs consistent emptying, ideally eight to twelve times in a 24-hour period, to stimulate the necessary production signals. Missing feeding or pumping sessions, especially during periods of separation, tells the body that less milk is needed.
Ineffective milk removal can also incorrectly signal low demand, even if the baby is feeding often. A poor latch, a tongue tie, or a similar anatomical issue can prevent the baby from efficiently draining the breast, leaving residual milk that contains FIL. When using a pump, an ill-fitting flange that is either too small or too large can cause ineffective emptying, leading to reduced milk output and pain.
Supplementing with formula without compensating by pumping quickly reduces the overall demand placed on the breasts. When a baby is full from a formula bottle, they nurse less, causing a lack of stimulation and incomplete emptying. The key principle for maintaining supply is that every missed feed or supplement must be replaced with a pumping session to ensure the breast is fully drained.
Hormonal and Medical Causes
A drop in milk supply can also be an internal physiological response triggered by hormonal shifts or underlying medical conditions. The successful transition to mature milk production after birth, known as lactogenesis II, requires a dramatic drop in the pregnancy hormone progesterone. If small pieces of the placenta remain in the uterus—a condition called retained placental fragments—they continue to secrete progesterone, which suppresses the action of the milk-making hormone prolactin. This hormonal interference can prevent the milk volume from ever fully increasing.
Endocrine disorders can also disrupt the delicate balance of hormones required for lactation. Hypothyroidism, a condition where the thyroid gland is underactive, is associated with low milk supply because thyroid hormones are necessary for prolactin and oxytocin to function optimally. Polycystic Ovary Syndrome (PCOS) may similarly affect supply due to insulin resistance and higher androgen levels, which can interfere with the milk production process.
Certain medications are known to negatively impact milk production by interfering with prolactin levels. Common decongestants containing pseudoephedrine, for instance, can significantly reduce milk volume by up to 24% after a single dose, likely by depressing prolactin secretion. Similarly, hormonal contraceptives that contain estrogen are known to lower prolactin and can cause a supply dip, especially if they are introduced before the milk supply has been fully established. Acute infections like mastitis or a severe illness such as the flu can also cause a temporary, localized reduction in milk supply as the body diverts resources to fight the illness.
Lifestyle and Environmental Factors
Chronic stress, anxiety, or lack of adequate rest can reduce the efficiency of the milk ejection reflex, or “let-down.” When the body experiences stress, it releases the hormone cortisol, which can block the action of oxytocin, the hormone responsible for triggering the milk to flow. If milk cannot be released efficiently, the breast is not fully emptied, and the supply-and-demand system incorrectly signals a need for less milk.
Severe dehydration is another factor that can impact milk volume, as breast milk is approximately 87% water. Although the body prioritizes milk production, significant fluid loss or insufficient intake can lead to a decrease in the volume of milk produced.
Extreme dieting or severe caloric restriction can also affect supply, though the relationship is less direct than once believed. While moderate weight loss typically does not impact milk volume or composition, insufficient caloric intake over an extended period can strain the body’s resources. Lactation requires an additional energy expenditure of roughly 500 calories per day, and a large, sustained deficit may eventually signal to the body that it cannot sustain full milk production.