Breast milk

Breast milk is the fluid produced by lactating mammary glands to nourish infants. Its composition changes over time and includes nutrients, immune factors, and living cells.

Colostrum: The first milk produced after birth, rich in antibodies and other protective components. This early form of breast milk is especially concentrated in immune factors.
Prolactin: A pituitary hormone that stimulates milk synthesis in the mammary glands. Its action supports ongoing production after lactation begins.
Breastfeeding: Feeding an infant directly from a lactating breast. It is the direct route by which infants commonly receive breast milk.
Infant immune system: The developing network of cells, tissues, and molecules that defends infants against infection. Milk’s antibodies and other bioactive components interact with this developing defense system.
Human milk research: Scientific study of human milk composition, production, and effects on infants and lactating people. Its many interacting components make breast milk a continuing subject of investigation.
Human milk oligosaccharides: Complex sugars in human milk that feed selected gut microbes and influence infant immunity. These abundant sugars help shape the infant gut microbiome without serving mainly as calories.
Oxytocin: A hormone that causes smooth-muscle contraction and supports milk ejection during breastfeeding. It triggers the let-down reflex that moves milk toward the nipple.
Expressed breast milk: Breast milk removed from the breast by hand or with a breast pump. Expression allows milk to be fed when direct nursing is not possible.
Necrotizing enterocolitis: A serious intestinal disease that primarily affects premature and medically fragile newborns. Human milk feeding is associated with lower risk among very premature infants.
Breastfeeding and cognition: Research examining associations between breastfeeding and cognitive development. Studies assess whether reported cognitive differences reflect milk, caregiving, or social factors.

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