Breast engorgement is the overfilling of the breasts with milk, which can happen when milk isn't being removed well from the breasts by breast-feeding, pumping, or expressing by hand. Severely engorged breasts become increasingly hard, swollen, and tender; the nipples and areolae can become hard and flattened, making it difficult for a baby to latch on to the breast properly.

If breast engorgement is severe and the breast is hard, the baby sucks but removes little milk. The breasts are stimulated to produce even more milk, increasing the swelling and engorgement. Breast engorgement most commonly occurs during the 2 to 5 days after childbirth, when a mother's milk supply is developing and her newborn has an irregular breast-feeding routine.

A mother with a regular breast-feeding routine can become engorged if she cannot nurse or pump as much as usual or suddenly stops breast-feeding. A mother who doesn't begin breast-feeding after childbirth will have several days of mild to moderate breast engorgement that gradually goes away when the breasts aren't stimulated to produce more milk.

Treatment to reduce pain and swelling includes applying ice or cold compresses and wearing a supportive nursing bra. Hard breasts can be softened by applying heat, massaging them gently, and using your hands to remove (express) a small amount of milk from both breasts.

Severe breast engorgement can cause a slight fever and tender lymph nodes in the armpits. Without treatment, severe engorgement can lead to blocked milk ducts and breast infection (mastitis).