As with all other organs and systems in their bodies, newborns’ immune systems are not fully developed at birth. Rather, their immunity—a protective function consisting of cells, proteins, and organs—grows and strengthens with time. With each new day, this immune system strives to keep them safe from the countless pathogens in their environment.
At birth, a baby’s immune system is still quite weak and sensitive. Given its fragility, nature has compensated for this by endowing mothers with the ability to transfer immunity to their baby (called passive immunity) by way of antibodies through breast milk. A mother’s breast milk is filled with protective immunoglobulins that work to fight off bacteria and viruses that could be harmful to the baby. This is why breastfed babies get sick much less often than formula-fed babies.
