Chronic endometritis is typically caused by an infection, which can result from a variety of sources. Common causes include bacterial infections such as those from bacterial vaginosis, sexually transmitted infections (STIs) like Chlamydia and Gonorrhea, and other pathogens such as Mycoplasma and Ureaplasma. Additionally, chronic endometritis can occur following pelvic inflammatory disease (PID), retained products of conception, or after gynecological procedures like hysteroscopy.