New parents often feel that their breasts are empty or not full any more. This anxiety often causes mothers to end exclusive breastfeeding prematurely or begin supplementing with formula when it is not needed. One of the most common misconceptions about breastfeeding is that breasts, like tanks or bladders, fill and empty. Here are some facts about the way human lactation works to help nursing mothers understand what is going on in there.

Fact: Breasts contain glands, not bladders. Milk production is continuous.
Human milk is made by specialized cells called myoepithelial cells. Blood is supplied to these cells, and they turn blood into milk, drop by drop. The milk is continuously being produced by these cell as well as continuously reabsorbed into the blood stream. During periods of engorgement, the body tries to reabsorb the milk faster and slow down the production. When the baby is actively nursing or mom is actively pumping, the reabsorption is slower and production is faster. Breasts can never be empty until after the baby is fully weaned off breastfeeding.

Fact: Babies don’t take all of the available milk during nursing.
Using ultrasound, science has determined that babies take about 65% of the available milk in the breast during a feeding session. This is why pumping milk after feedings is recommended for mothers who are pumping and storing milk for future separations.

Fact: The more rapidly milk is removed from the breast, the more rapidly new milk is made.
When milk is being removed from the breast, the milk making hormone prolactin is highest. Frequency of nursing and pumping is key to making more milk. Women who “save up” or try to wait for the breast to feel full before nursing are actually lowering their prolactin levels. This is why supply and demand is the law for breastfeeding and making more milk. Moms who remove milk the most frequently will make the most breastmilk.

Fact: Even a hospital grade double electric breast pump cannot empty the breast.
Because milk making hormones peak during milk removal (nursing, pumping, or hand expression), the body will always rush to make more milk every time mom is pumping.

The Take Away

Continuous breastfeeding or breast milk removal is the key to high levels of milk production. If a mother is doubting her milk production capabilities, milk production is easily assessed by an IBCLC at a home visit or even via telehealth. IBCLCs employ techniques like weighed feeds and latch assessments to determine how well the baby is “transferring” or getting enough milk. When in doubt, it is always better to nurse more and pump more, and add hand expression. Supply and demand is the ruling principle of lactation. Feelings of fullness do not happen for all women who make a full milk supply. Feelings of fullness may come and go but do not indicate milk production levels or how well the baby is eating.