Lactogenesis II

What happens when the milk “comes in”?

Typically, between Day 2 and Day 4 after delivery, breasts stop making colostrum and start making milk. This is called lactogenesis II, or milk “coming in.” The breasts may become heavier, larger, and tender. This can be uncomfortable, but it is a sign of a good milk supply. The discomfort is usually relieved by breastfeeding the baby when the baby is hungry. If the baby struggles to breastfeed or the mother has not expressed effectively soon after birth, her breasts may become hard and uncomfortable.

A) Describing the milk coming in

The making of colostrum, transitional milk, mature milk, and weaning milk is called lactogenesis. Lactogenesis is divided into four stages based on the type of milk made. These are usually written using latin numbers (I, II, III, IV).

Between 24 to 96 hours (average 60 hours) after delivery, the breasts switch from making colostrum to making milk (Dewey 2003; Kent 2007). This can be called lactogenesis II, secretory activation, or milk “coming in”.

The breast makes transitional milk until the end of the second week after delivery and then it changes to making mature milk (lactogenesis III).

B) Signs of milk coming in

There are several signs that indicate that the milk is coming in and these can be helpful when assessing the amount of milk a mother is able to make.

1) The breasts feel different

To make milk, a lot of blood must flow to the breasts. The breasts will also now hold milk until the baby breastfeeds. All this activity may result in breasts that are:

  • Heavier
  • Larger
  • Tender with lumps throughout
  • Fuller
  • Firmer

While it can be a little uncomfortable, filling is a good sign. Mothers who have a lot of filling tend to have a very good milk supply.

There is a range of fullness for normal breasts as the milk comes in. Smaller breasts can get quite full, while mothers with larger breasts may not notice as much filling.

Breastfeeding effectively when the baby is hungry is usually all that is needed to settle the discomfort of milk coming in.  

2) Clear colostrum is replaced by creamy milk

As the milk comes in, the clear, yellow colostrum has been replaced by a yellowish, creamy milk.

3) Milk is produced in larger amounts

As the milk comes in, it is present in larger amounts. Mother may notice:

4) Armpit swelling

Sometimes there is breast tissue in the mother’s armpit and, when the milk comes in, this tissue will fill as well. The mother will feel lumps in her armpits and these can range in size. Other than being tender, these are generally harmless and are a sign of a good milk supply. They show there is a lot of milk tissue and that it is responding well to the birth of the baby.

C) Problems with milk coming in

If after birth, the baby has struggled to breastfeed or the mother has not expressed effectively, her breasts may become extremely hard and uncomfortable and even engorged.

If a mother's breasts don’t undergo any of the changes described above, she may have a low milk supply or her milk may be coming in late (on or after Day 5).


Dewey KG, Nommsen-Rivers LA, Heinig MJ, et al. Risk factors for suboptimal infant breastfeeding behavior, delayed onset of lactation, and excess neonatal weight loss. Pediatrics. 2003 Sep;112(3 Pt 1):607-19
Kent JC. How breastfeeding works. J Midwifery Womens Health. 2007 Nov-Dec;52(6):564-70