What causes autoimmune diseases?

Why the immune system becomes misdirected remains unknown. However, several factors may influence the development of an autoimmune disease. For example, a genetic predisposition is mandatory.

Although autoimmune diseases are not genetic diseases, a genetic predisposition is mandatory for the development of such a disease. This means certain combinations of genes lead to a higher risk than others of developing an autoimmune disease.

In addition to genetic predisposition, various environmental factors are necessary. They are the trigger that finally turns the immune system on. 
Infections, vaccinations or immunizations, hormonal changes, smoking and nutritional deficiencies are among the environmental factors that may provoke an autoimmune reaction.

Autoimmune diseases cannot be caught from another person.