Why are autoimmune disorders are considered so dangerous?

They destroy tissues: Autoimmune disorders arise from an overactive immune system in which the body attacks its own tissues. The different types & the amount of destruction that occurs depends on the kinds of tissues targeted. Some affect a single organ (as in thyroiditis) while others involve multiple areas (such as lupus). If not diagnosed & treated, these disorders progressively worsen health & may hasten death.

Autoimmunity: Because the bodies on defense system (antibodies) are attacking itself and recognizing "self" as foreign.....Which is very dangerous.