Breastfeeding

Breastfeeding, or nursing, is the practice of feeding an infant or toddler breast milk. This can happen directly from the breast or by using a pump to extract milk for later feeding. The World Health Organization advises starting breastfeeding within the first hour after birth and feeding on demand. For the first six months, exclusive breastfeeding—meaning no other food or drink except vitamin D supplements—is recommended. After that, the WHO suggests continuing breastfeeding alongside appropriate solid foods for up to two years or longer. Globally, between 2015 and 2020, only about 44% of infants were exclusively breastfed for their first six months.

Breastfeeding offers health advantages for both mother and child that infant formula does not. If breastfeeding rates in low- and middle-income countries rose to near-universal levels, roughly 820,000 deaths of children under five could be prevented each year. For babies, breastfeeding lowers the risk of respiratory infections, ear infections, sudden infant death syndrome (SIDS), and diarrhea in both wealthy and poorer nations. It may also reduce the chances of asthma, food allergies, and diabetes, and could support cognitive development and lower the risk of obesity later in life.

For mothers, immediate benefits include less blood loss after delivery, better uterine contractions, and a lower risk of postpartum depression. Breastfeeding delays the return of menstruation and, under specific conditions, fertility—a state called lactational amenorrhea. Long-term, it reduces the risk of breast cancer, cardiovascular disease, diabetes, metabolic syndrome, and rheumatoid arthritis. While breastfeeding is cheaper than formula, the effect on a mother’s ability to earn income is often left out of cost comparisons. Common early symptoms include vaginal dryness, De Quervain syndrome, cramping, mastitis, moderate to severe nipple pain, and a sense of lost bodily autonomy. These issues usually peak at the start and become more manageable after a few weeks.

Feedings can last 30 to 60 minutes at first, as milk supply builds and the infant learns the suck-swallow-breathe pattern. As supply increases and the baby becomes more efficient, feedings shorten, and older infants may nurse less often. If direct breastfeeding isn’t possible, expressing or pumping to empty the breasts helps prevent plugged ducts and infections, maintains milk supply, relieves engorgement, and provides milk for later feeding. Medical conditions that prevent breastfeeding are rare. Mothers using certain recreational drugs should avoid breastfeeding, but most medications are safe. Current evidence suggests COVID-19 is unlikely to pass through breast milk. Smoking tobacco or consuming small amounts of alcohol or coffee are not reasons to stop breastfeeding.

**Breastfeeding Physiology**

Breast development begins at puberty with the growth of ducts, fat cells, and connective tissue. Breast size is determined by fat cells and does not affect a mother’s ability to breastfeed or her milk volume. Milk production, called lactogenesis, happens in three stages. The first stage occurs during pregnancy, developing breast tissue and producing colostrum—a thick, nutrient-rich early milk low in volume. The birth of the baby and delivery of the placenta trigger the second stage, when milk “comes in” over several days. The third stage develops gradually over weeks, with a full milk supply regulated locally at the breast, mainly by the infant’s demand. This differs from the second stage, which is controlled centrally by hormone feedback loops after the placenta is expelled. Lactation can also be induced without pregnancy through hormone therapy and nipple stimulation.

**Lactogenesis I and Other Pregnancy Changes**

Around the 16th week of pregnancy, hormonal changes prepare the breasts for lactation. This phase, Lactogenesis I, is driven by estrogen, progesterone, and prolactin from the placenta and brain. These hormones cause structural growth of milk-producing alveolar tissue and the production of colostrum. Prolactin is the main hormone for milk production, but high progesterone levels during pregnancy block prolactin receptors, preventing milk from fully coming in until after birth. Other changes under progesterone and estrogen include blood vessel dilation, increased uterine blood flow, higher glucose availability for the fetus, and skin pigmentation changes like darkening of the nipples and areola, the linea nigra, and melasma. From about 16 weeks, small amounts of straw-colored colostrum may leak from the nipples.