Your immune system is the first line of defense against foreign invaders such as viruses, bacteria, fungi and toxins. When that system doesn't work, it can throw your whole body into disarray.
An autoimmune disease occurs when the immune system doesn't respond to these outside invaders as it should. There are more than 100 types of autoimmune diseases, and nearly every part of your body can be affected by abnormal immune system reactions.
People of all genders can be affected by an autoimmune disease, but they occur more often in women, according to a 2020 review published in the journal Cureus. Autoimmune disorders are often difficult to diagnose because of the wide variety of symptoms, and that means the number of affected individuals is likely much higher than reported.