Hormonal Imbalance: This is often the most common cause of vaginal bleeding in non-pregnant women, particularly those of reproductive age. Hormonal fluctuations can lead to irregular menstrual cycles, ovulation disorders, or anovulatory cycles, resulting in abnormal uterine bleeding.

Uterine Fibroids: These are common benign tumors that can cause heavy or irregular menstrual bleeding, and are often found in women of reproductive age.
Endometrial Hyperplasia: This condition involves the thickening of the uterine lining, which can lead to abnormal vaginal bleeding. It's more common in perimenopausal or postmenopausal women.
Polycystic Ovary Syndrome (PCOS): A hormonal disorder that can cause irregular periods, leading to vaginal bleeding at unexpected times.
Infection or Inflammation: Conditions like pelvic inflammatory disease (PID), cervicitis, or vaginitis can cause vaginal bleeding.

Endometrial Cancer: Although less common, endometrial cancer is a critical diagnosis to consider, especially in postmenopausal women with vaginal bleeding. It requires prompt investigation and treatment.
Cervical Cancer: Abnormal vaginal bleeding can be a symptom of cervical cancer, making it essential to not miss this diagnosis, particularly in women who have not had regular cervical screening.
Bleeding Disorders: Conditions like von Willebrand disease can cause heavy or prolonged menstrual bleeding.

Uterine Arteriovenous Malformation (AVM): A rare condition where there's an abnormal connection between arteries and veins in the uterus, which can cause vaginal bleeding.
Uterine Sarcoma: A rare type of cancer that originates in the muscle and supporting tissues of the uterine walls.
Genetic Disorders: Certain genetic conditions can affect the reproductive system and lead to abnormal vaginal bleeding, though these are relatively rare.