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.