What is Lactation?

Medically Reviewed by Dan Brennan, MD on July 24, 2022
5 min read

If you’re pregnant, it doesn’t matter if you’ve decided to nurse your baby or formula feed. You’re likely going to lactate anyway. However, not every pregnant person can lactate, and some non-pregnant people can. The mechanisms that trigger lactation are truly amazing.

Lactation is the process of producing milk from your mammary glands to feed your young, and almost all mammals do it. The lactation process typically begins in pregnancy and continues until you stop expressing milk. Although it's most common to lactate during pregnancy and after giving birth, it’s possible to induce lactation outside of those conditions.

The lactation process begins with hormones. These hormonal changes that cause lactation are part of a process called lactogenesis, which has three stages.

Stage I lactogenesis (secretory initiation). The first stage of lactogenesis begins sometime after your 16th week of pregnancy and continues throughout the second half of pregnancy. During this stage, your estrogen and progesterone levels rise and cause changes to your breasts:

  • You grow more milk ducts, causing your breasts to look and feel fuller.
  • Your nipples may darken, and your areolas, the areas around your nipples, may get larger.
  • The Montgomery glands, which are the small bumps on your areola, start to secrete an oil to lubricate your nipples.
  • Your body begins to make colostrum, the nutritious first milk for your baby. It’s possible to start lactation during pregnancy, and you can begin to leak colostrum before giving birth as your body prepares.

Stage II lactogenesis (secretory activation). The second stage of lactogenesis occurs after giving birth. When the placenta is delivered or removed, your progesterone levels drop. This leads to elevated levels of prolactin, cortisol, and insulin, which stimulate your body so you begin producing milk. Prolactin is a milk-producing hormone.

About 2 or 3 days after delivery, your milk will “come in.” Your breasts may swell, and you’ll notice a sharp increase in milk production. Engorgement, or the feeling that your breasts are overly full, may occur, causing sore or tender breasts.

Stage III lactogenesis. Some people believe there to be a stage III of lactogenesis, which refers to the rest of your time lactating. 

Nursing, also called breastfeeding or chestfeeding, is the term used for when your baby drinks from your breast or chest. Your nipples are full of nerves, and when your baby suckles, those nerves tell your body to release prolactin and the hormone oxytocin. Prolactin produces the milk, and oxytocin causes the muscle contractions that allow the milk to flow through the milk ducts.

After your baby has suckled for about 30 seconds, you’ll experience “let down.” This term describes the milk being released. Your body will try to replace the same amount of milk you release, whether you’re nursing or pumping. For the most part, lactation will continue until you stop expressing milk.

Science has made it possible to lactate without pregnancy, but you’ll still need the right hormones. If you need to induce lactation, you'll be given medication to mimic the hormones typically released during pregnancy and after delivery. However, it’s not always this simple and sometimes requires working alongside an experienced healthcare provider.

Several factors may impact your ability to lactate, including:

  • Poor or insufficient nutrition
  • Certain medications, including dopamine agonists like pramipexole and ropinirole
  • Hormonal imbalances
  • Trauma or surgery to your breasts or nipples, including breast augmentation and reduction
  • A history of radiation therapy
  • Some medical conditions
  • Using drugs or alcohol

Lactation requires your body to undergo massive hormonal changes. This means that it can be rough on you both physically and mentally. Be on the lookout for some of these side effects and conditions.

Engorgement. As mentioned above, engorgement is the feeling of your breasts being overly full, leading to tenderness and soreness. Engorgement is common when your milk first comes in as your body adjusts to the amount of milk it needs to produce. But you may also experience engorgement if you find yourself unable to express milk on schedule.

This can happen with a change in routine, such as your baby starting baby foods or if you go back to work. To prevent engorgement, try to plan ahead by planning to pump if you aren’t able to nurse your baby. If you become engorged, a warm shower or compress can help relieve the pressure before nursing or pumping.

Mastitis. Mastitis is an inflammation of breast tissue that most often happens during lactation. Although mastitis doesn’t always indicate an infection, infection is a very common cause. The inflammation caused by mastitis may cause pain, swelling, redness, and warmth over the infected area. Mastitis may also be accompanied by fever and chills.

The main cause of lactation mastitis is a blocked milk duct. This can happen if you don’t fully empty your breasts when feeding or pumping. Because of the pain and misery mastitis causes, it may be tempting to abandon lactation altogether. But the best solution for mastitis caused by a blocked milk duct is to continue feeding or pumping.

Mastitis can also be caused by bacteria. These bacteria can enter your breast either through the opening of a milk duct while your baby feeds or through broken skin if your nipples are cracked. This type of mastitis won’t improve by feeding or pumping, but it's still safe to do those things while you recover. 

Regardless of the type of mastitis, the typical treatment is over-the-counter pain relievers and antibiotics if an infection is present. To avoid mastitis, drain both breasts fully at each feeding or pumping session and try to vary your feeding positions, if applicable.

Dysphoric milk ejection reflex. Also called D-MER, dysphoric milk ejection reflex is an emotional “drop” that happens during the letdown stage of lactation. It can cause temporary feelings of depression, anxiety, and hopelessness and a range of other negative emotions.

D-MER is not postpartum depression, but the two are hormonally related. Specifically, D-MER is caused by a drop in the feel-good neurotransmitter dopamine. For letdown to happen, your body needs your prolactin levels to rise. Because dopamine keeps prolactin in check, dopamine has to fall, but sometimes it falls inappropriately. When that happens, you can feel a temporary, but dark, crash. 

The only treatment for D-MER is medications that stabilize dopamine levels, but these are often a last resort.