Autoimmune diseases—a diverse class of conditions caused by an errant immune system—are scary, often debilitating, and sometimes deadly. And for reasons that researchers don’t fully understand, cases seem to be rising precipitously, especially among people over age 50. Recent research shows these conditions are 50 percent higher in older adults than they were 25 years ago.

Researchers think one factor could be changing environment and lifestyles. More exposure to chemicals, processed foods, and additives in our diets are totally different to what humans used to eat. Sedentary lifestyles and obesity may also be a factor.

“With an autoimmune disease, your immune system attacks healthy tissues and structures in your body,” says Timothy Niewold, MD, director of NYU Langone’s Judith and Stewart Colton Center for Autoimmunity. “These normal defenses, which work to keep viruses and bacteria at bay to prevent illness, have essentially gotten confused and set off friendly fire against your own body.”

Approximately 23.5 million people in the United States have an autoimmune disorder, according to the National Institute of Environmental Health Sciences. Some are mild and manageable while others are life altering. The most common autoimmune disorders in the United States are Crohn’s disease, type 1 diabetes, multiple sclerosis (MS), rheumatoid arthritis, Hashimoto’s thyroiditis, celiac disease, and psoriasis.

Read more from AARP.