Pelvic inflammatory disease (PID) typically originates from sexually transmitted infections (STIs) such as chlamydia, gonorrhea, or Mycoplasma genitalium. These infections cause bacteria to ascend from the vagina into the upper reproductive organs, including the uterus, fallopian tubes, and ovaries. Normally, the cervix acts as a protective barrier, preventing bacteria from advancing deeper into the reproductive system. However, certain infections can disrupt this cervical function, allowing bacteria to move upward and lead to the development of PID.