Dysfunction of the immune system is termed as immune disorder. These disorders can be characterized in several different ways:
- By the component(s) of the immune system affected
- By whether the immune system is overactive or underactive
- By whether the condition is congenital or acquired
International Union of Immunological Societies has characterized that, there are more than 150 primary immunodeficiency diseases (PIDs). However, the number of acquired immune-deficiencies exceeds the number of PIDs and suggested that most people have at least one primary immunodeficiency, due to redundancies in the immune system.