Under normal conditions, an immune response cannot be triggered against the cells of one's own body. In certain cases, however, immune cells make a mistake and attack the very cells that they are meant to protect. This can lead to a variety of autoimmune diseases. They encompass a broad category of over 100 diseases in which the person's immune system attacks his or her own cells and tissue.

The exact mechanisms causing these changes are not completely understood, but bacteria, viruses, toxins, and some drugs may play a role in triggering an autoimmune process in someone who already has a genetic (inherited) predisposition to develop such a disorder. It is theorized that the inflammation initiated by these agents--toxic or infectious--somehow provokes in the body a "sensitization" (autoimmune reaction) in the involved tissues.

As the disease develops, vague symptoms start to appear, such as joint and muscle pain, general muscle weakness, possible rashes or low-grade fever, trouble concentrating, or weight loss. Numbness and tingling in hands and feet, dry eyes, hair loss, shortness of breath, heart palpitations, or repeated miscarriages may also indicate that something is wrong with the immune system.