Question: how does immune system work

Erin Pallott answered on 13 Jan 2026:

The immune system is a big network of different cells and tissues! To break its whole job down into parts:
– Barrier sites: These are more passive, effectively preventing pathogens getting in and stopping you getting sick in the first place. Your skin, gut, lungs and more have immune cells living underneath the barriers ready to catch things early.
– Innate Immune System: Your innate immune cells patrol the body and attack harmful cells or pathogens in broad ways, such as releasing harmful chemicals to destroy them. These cells will deal with threats in a similar way every time.
– Adaptive Immune System: These are immune cells created to directly match the specific threat at hand, but it takes a few days to get started. They have receptors that will match parts of a virus, bacteria, cancer cell or other harmful things, and direct responses to either kill or eject the threat.
– Memory: Your immune system reserves a few of your adaptive immune cells as memory immune cells. The patrol the body for many years, and if they recognise a threat from a previous time, they can call on the adaptive immune system to activate much faster than before, so it can get rid of the threat before you even feel sick! This is why you don’t get things like chicken pox more than once.