Lactation (Human Milk Production): How it Works (2024)

What triggers lactation?

A series of hormonal events, which begin when you’re pregnant, trigger the lactation process. That process is called lactogenesis.

Stage one lactogenesis: This begins around the 16th week of pregnancy and lasts until a few days after you give birth.

• Estrogen and progesterone rise and cause your milk ducts to grow in number and size. This causes your breasts to become fuller. Your mammary glands begin to prepare for milk production.
• Your nipples darken and your areolas become larger.
• Your Montgomery glands (small bumps on the areola) secrete oil to lubricate your nipple.
• Your body begins making colostrum. It’s highly nutritious and filling and serves as your baby’s first milk.

Stage two lactogenesis: This stage starts about two or three days postpartum (after giving birth). It’s when milk production intensifies.

• Once your baby and placenta are delivered, a sudden drop in your estrogen and progesterone causes the hormone prolactin to take over.
• Prolactin is the hormone that produces milk.
• You’ll notice your milk production increases dramatically at this stage. It’s often referred to as milk “coming in.”
• Your breasts are often engorged (or overly full of milk) to the point where they feel sore, painful or tender.

Stage three lactogenesis: This describes the rest of the time you lactate.

• Lactation generally continues as long as milk is removed from your breast.
• The more milk that’s removed, the more milk your body makes to replace it. Frequent feeding or pumping will cause your body to make more milk.

Hormones for lactation

The hormone prolactin controls the amount of milk you produce, and your body begins producing prolactin early in pregnancy. At first, the high levels of estrogen, progesterone and other pregnancy hormones suppress prolactin. Once you deliver the placenta, those pregnancy hormones drop and prolactin takes charge.

When your baby suckles, it stimulates nerves that tell your body to release prolactin and oxytocin. Prolactin causes the alveoli to make milk and oxytocin causes muscle contractions that push out of the alveoli and through the milk ducts.

When milk is released, it’s called a “letdown,” and it takes about 30 seconds of suckling before the letdown occurs. Because you can’t control which breast receives the hormones, the letdown can cause milk to drip from both nipples.

Inducing lactation in people who aren’t pregnant requires medication that mimics hormones your body makes during pregnancy. Suckling from the nipple can initiate lactation, either with a breast pump or by a baby. This is a complex process that involves working closely with a healthcare provider who understands the needs of non-pregnant people and has experience initiating lactation.

When do you lactate during pregnancy?

Lactation begins as early as a few weeks into the second trimester of your pregnancy. As estrogen and progesterone levels rise, your body prepares for lactation by increasing the number of milk ducts in your breasts, and those milk ducts will transport milk from the alveoli to your nipples. About midway through pregnancy, your body creates colostrum, which is your baby’s first milk.

Can you lactate when you’re not pregnant?

Yes, it’s possible to lactate if you’re not pregnant. Inducing lactation is a complex process that usually involves using hormone-mimicking drugs for several months to produce milk. The second part of lactation is expressing the milk through your nipple. Stimulation from infant suckling, pumping with a breast pump or hand-expressing signals the brain to release the milk. It’s common for people in this situation to receive assistance from a healthcare provider who understands the needs of non-pregnant people and has experience initiating lactation.

How do you stop lactation?

There are many reasons why you might need to stop producing milk, and you can stop lactating either naturally or with the help of hormonal drugs.

Natural milk suppression

Lactation is a supply-and-demand process. Your milk supply gradually goes down as your baby relies less on breast milk, or as you reduce the number of times you nurse or pump. Generally, if you decrease the volume of milk removed from your breasts, your body will slow milk production.

Suppressing your milk can feel uncomfortable and most people will become engorged (the term for overfilled breasts). You may also leak milk or develop a clogged milk duct. However, you can treat that pain by taking an over-the-counter pain reliever, wearing a firm bra or using an ice pack on your breasts.

Medication suppression

Medications can also be an option if you need to stop producing milk. Your healthcare provider can explain more about lactation-suppressing drugs, as well as the benefits and possible side effects.