Although it is unknown what causes most types of vasculitis, immune system abnormality, inflammation of blood vessels, and genetic factors appear to be somewhat important in the cause of the disease. Vasculitis can also be caused by an immune or allergic reaction in the vessel walls.
Allergic reaction: The hypersensitive response of the immune system of an allergic individual to a substance. When an allergen enters the body, it causes the body's immune system to develop an allergic reaction in a person with an allergy to it. This reaction can occur when the immune system attacks a normally harmless substance (the allergen). The immune system calls upon a protective antibody called immunoglobulin E or IgE to fight these invading substances.
Allergy: An allergy is an exaggerated immune reaction to substances that are normally harmless. Allergy can appear in many forms and cause many symptoms, such as sneezing, respiratory symptoms such as asthma or hay fever, itching, skin rashes, or generalised reaction such as anaphylaxis.