There is no definitive answer as everyone's circumstances are unique. However, some common causes of autoimmune diseases have been identified. These include genetics, environmental factors, and infections. Autoimmune disease occurs when the body's immune system attacks healthy cells, tissues, and organs. Several different factors can cause this. Genetics plays a role in many autoimmune diseases, meaning that if you have a family member with an autoimmune disorder, you are more likely to develop one yourself.  Environmental factors such as stress, exposure to toxins, and certain infections can also trigger the development of autoimmune diseases. Additionally, some autoimmune diseases are caused by malfunctions in the body's regulatory T cells, which ensure that the immune system does not attack healthy tissues.