What does our immune system do?

As long as your immune system is working well, you probably won’t even notice that it is there. ^1b Its function is to protect our bodies from disease causing organisms, or pathogens, such as bacteria, viruses and fungi, as well as from cell changes that can make us sick. ^{1a, 2a} It is vital for our health and survival. ^2a

If your immune system is no longer working optimally because it is weak or because you have been exposed to a particularly aggressive pathogen, then you will become sick. If you are exposed to a new pathogen that you have never been in contact with before, you are also likely to become ill. ^1b

Our immune systems can be divided into two systems which work together whenever a pathogen or harmful substance triggers an immune response in the body. ^1c

The innate immune system fights against harmful substances and pathogens that enter the body using immune cells which attack the pathogens. ^1d  

The adaptive immune system is slower and makes antibodies to fight pathogens that the body has previously come into contact with. This explains why you only get some diseases like childhood chickenpox once – the body has the antibody to fight it the second time you come into contact with it. ^{1d, 2c}

Everyone’s immune system is different but usually our immune systems become stronger as adults, as we have been exposed to more pathogens and developed more immunity. As a result of the increased immunity, teenagers and adults tend to get sick less often than children. ^2b

If our immune systems are compromised, we are more prone to infections, and it is harder to fight these infections. ^{3a, 4b}