The immune system or immune system contributes to the maintenance of the integrity of the individual by removing external substances or infectious agents to which the individual is exposed. It is also able to discern between healthy and unhealthy normal cells and to recognise "danger" signs that may affect the body.

Viruses, for example, can be spread through the air, by contact with secretions or through water, among other ways. The immune system detects this virus, activating all its "machinery" to prevent transmission and prepare the body for both combat and recovery.

It is a system as complex as the nervous system, so its optimal state is key to effective defence and action against external aggression. The immune system is present both outside our bodies, in our skin and our tears, as well as inside us. There, it is found in cells, such as white blood cells, and as organs that provide defence elements such as the tonsils, spleen, lymph nodes and the entire mucosa covering our digestive tract.