Hemorrhoids: This is often the most common cause of bright red blood per rectum, especially if the bleeding is associated with bowel movements. Hemorrhoids are swollen veins in the lowest part of the rectum or anus, and they can bleed when irritated.

Anal Fissure: A tear in the lining of the anus can cause bright red bleeding, especially during or after bowel movements. The pain associated with an anal fissure can help differentiate it from hemorrhoids.
Diverticulosis: This condition involves the formation of small, bulging pouches (diverticula) in the digestive tract. When these pouches bleed, they can cause bright red blood per rectum, though the bleeding is often more significant and can be associated with diverticulitis.
Rectal Ulcer: Ulcers in the rectum can bleed and cause bright red blood per rectum. These ulcers can be due to various causes, including inflammatory bowel disease (IBD), infections, or solitary rectal ulcer syndrome.

Colon Cancer: Although less common than other causes, colon cancer can present with bright red blood per rectum, especially in older adults. It's crucial to not miss this diagnosis due to its significant implications for treatment and prognosis.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause rectal bleeding, among other symptoms. Early diagnosis and treatment are vital to manage the disease and prevent complications.
Angiodysplasia: These are vascular malformations in the colon that can cause bleeding. They are more common in older adults and can be a significant cause of gastrointestinal bleeding if not identified and treated.
Gastrointestinal Infection: Certain infections, such as those caused by Salmonella or Shigella, can lead to rectal bleeding. Identifying and treating the underlying infection is crucial.

Arteriovenous Malformation (AVM): AVMs are abnormal connections between arteries and veins that can occur in the gastrointestinal tract and cause bleeding.
Dieulafoy's Lesion: A rare cause of gastrointestinal bleeding, characterized by a small mucosal defect with an exposed, often large, caliber artery at its base.
Intussusception: Although more common in children, intussusception (the telescoping of one segment of intestine into another) can occur in adults and cause rectal bleeding, among other symptoms.
Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause bleeding, especially in children and young adults, due to the presence of ectopic gastric mucosa.