Research suggests that infection or toxic substances in your body can trigger it. Your immune system overreacts to these triggers and sets off the disease.

Experts consider adult-onset Still’s disease an auto-inflammatory condition because the immune system plays a role in its symptoms. At birth, you have an innate immune system. As you age, you form an adaptive immune system. That deals with the bacteria and viruses that get by your innate one.

When you have an autoimmune disease, your symptoms happen because your adaptive immune system overreacts and attacks your healthy cells and tissues. In auto-inflammatory diseases like adult-onset Still's disease, the innate immune system overreacts and causes inflammation.

Research also shows that people with adult-onset Still’s disease have higher levels of proteins called cytokines than people who don't have the disease.

Your immune system sends out cytokines to fight inflammation in the body.