Hemorrhoids: This is often the most common cause of rectal bleeding, especially in adults. Hemorrhoids can be internal or external and are usually caused by increased pressure on the veins in the rectal area, often due to constipation, straining during bowel movements, or pregnancy.

Diverticulosis: A condition where small, bulging pouches (diverticula) develop in the digestive tract, most commonly in the colon. These can bleed, especially if they become inflamed or if a blood vessel in a diverticulum bursts.
Anal Fissures: Small tears in the lining of the anus, which can cause pain and bleeding during and after bowel movements.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic inflammation and ulcers in the digestive tract, leading to rectal bleeding.
Gastrointestinal Infections: Certain infections, such as those caused by bacteria, viruses, or parasites, can lead to rectal bleeding, especially if they cause inflammation or ulcers in the rectum or colon.

Colorectal Cancer: Although less common than other causes, colorectal cancer is a critical diagnosis not to miss due to its potential for severe outcomes if not treated early. Rectal bleeding can be an early sign, especially in older adults.
Ischemic Colitis: Reduced blood flow to the colon can cause inflammation and potentially lead to bleeding. This condition requires prompt diagnosis and treatment to prevent complications.
Intussusception: A condition where a part of the intestine slides into an adjacent part, potentially cutting off blood supply and causing bleeding. It's more common in children but can occur in adults, often associated with a lead point like a tumor.
Angiodysplasia: Vascular malformations in the colon that can cause bleeding, often in older adults.

Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause bleeding, usually in children and young adults, due to the presence of ectopic gastric mucosa.
Solitary Rectal Ulcer Syndrome: A condition characterized by ulcers in the rectum, often associated with chronic constipation and straining during bowel movements.
Radiation Proctitis: Inflammation and damage to the rectum caused by radiation therapy, which can lead to bleeding.
Vasculitis: Inflammation of the blood vessels that can affect the gastrointestinal tract and cause bleeding, though this is a rare cause of rectal bleeding.