They are morbid conditions caused by the immune system attacking the body's tissues and organs. They are predominantly diseases of women of reproductive age. They can affect a single organ (organ-specific) or multiple organs simultaneously or sequentially (systemic). 

The scientific community has so far recognized over a hundred diseases that meet the criteria to be called autoimmune diseases. Some of these diseases are common, while others are rare. Studies have estimated that thirty-six million Europeans suffer from autoimmune diseases. These diseases constitute the second leading cause of morbidity and the third leading cause of disability among all diseases.