The immune system is like the police force of the body, attacking foreign factors that cause health problems, including viruses, bacteria, parasites, and allergens.
It is made up mainly of special types of cells in the blood, called white blood cells, which move around the body and protect vulnerable places, such as the nose, mouth, throat (e.g. tonsils), lungs, gut and broken skin. Further protection from inside the gut is provided by the microbiome.
The immune system starts to switch on from the moment of birth. Infants receive factors from mother’s milk that activate and support immune system functions. As children grown, they pick up all kinds of factors from the environment, other kids and adults.
Babies get sick almost three times more frequently than preschoolers . This is because the immune system gradually improves its ability to recognize infectious factors over time through exposure, using a process called “natural immunity”, or “acquired immunity”.