There are four categories of immune system disorder as follows:

• immunodeficiency disorders (primary or acquired) – this is when a part of the immune system is absent or is not working properly. When a person is born with an immunodeficiency it is called a primary immunodeficiency. Secondary immunodeficiencies are acquired through infection or reactions to drugs.

• autoimmune disorders (in which the body's own immune system attacks its own tissue as foreign matter) – this is when the boy’s immune system attacks it’s own healthy tissue and organs, mistaking them for foreign invaders. Some examples are Lupus, Rheumatoid arthritis, Scleroderma, Ankylosing spondylitis and dermatomyositis.

• allergic disorders (in which the immune system overreacts in response to an antigen) – this is when the immune system over reacts to exposure to antigens in the environment (which are known as allergens). The response is often seen in such symptoms as watery eyes and sneezing. Asthma and Eczema are common allergic disorders.

• cancers of the immune system – when the cells of the immune system grow out of control, cancers can result. Lymphoma and Luemia are two common types of such cancer.