Autoimmune diseases are those in which the immune system turns against the body it is supposed to protect (“auto” means “self”), attacking healthy cells and tissues. They’re the medical equivalent of friendly fire, and they can cause serious damage.

There are 50 known autoimmune diseases affecting two million Canadians, says Dr. Edward Keystone, director of The Rebecca MacDonald Centre for Arthritis and Autoimmune Diseases at Mt. Sinai Hospital in Toronto. Autoimmunity disproportionately affects women; ratios vary by disease, but overall, almost 80 percent of people with autoimmune disorders are female.  

While we don’t yet understand the causes of autoimmunity or how to cure it, “there is a huge sense of optimism,” says Dr. Keystone. Researchers are learning more about the immune system and why it becomes overactive, including the role of genetics. New medications for certain diseases, including lupus and rheumatoid arthritis, target specific problems in the body, acting like “guided missiles”—an improvement over the “carpet bombing” approach of older therapies. “The truth is,” says Dr. Keystone, “this is the most exciting time in the history of the treatment of autoimmune diseases, in terms of new therapies and improving patients’ outcomes.”

Here’s a look at some of the autoimmune diseases that affect Canadians: