Reactive arthritis is a type of arthritis that an infection in the body can trigger. Most commonly, a sexually transmitted infection or bacterial infection in the intestines triggers development of reactive arthritis.It’s considered to be an autoimmune disease of the spondyloarthritis group. The arthritis often doesn’t develop until after the infection has been successfully treatedPeople with reactive arthritis often experience symptoms in the larger joints of the lower extremity. Reactive arthritis was previously known as Reiter’s syndrome, a triad of arthritis, eye inflammation (conjunctivitis), and urinary tract inflammation (urethritis).The condition was previously thought to be uncommon. According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), men develop reactive arthritis more often than women, but the diagnosis is more difficult in women. The average age of onset is 30 years old. Men also tend to experience more severe joint pain than women.