Autoimmune disease is a chronic inflammatory condition where the immune system causes organ or systemic damage to the host. There are many autoimmune diseases that affect 7–9% of the population. Apart from adult-onset diabetes, which affects males more than females, and childhood diseases, which are proportionate across the sexes, the prevalence of autoimmune diseases in females is generally much higher—more than 85% in thyroiditis, systemic sclerosis, systemic lupus erythematosus (SLE) and Sjögren's syndrome patients and up to 60–75% in multiple sclerosis and rheumatoid arthritis (RA) patients. Autoimmune diseases are one of the 10 leading causes of death in women aged under 65 years in the United States.
Different body systems may be involved in different autoimmune diseases, however, they are generally characterised by chronic inflammation with a loss of tolerance to self-(auto)antigens, which are immune cells that attack the host. The cause for this loss of tolerance—the shift from normal immune function to autoimmune pathology—is poorly understood. It is generally agreed upon that the cause is multifactorial, involving a combination of genetic, environmental, hormonal and immune factors.