Hemorrhoids: This is the most common cause of rectal bleeding, especially in adults. Hemorrhoids can be internal or external and are often associated with straining during bowel movements, constipation, 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 to consider, especially in individuals over 50 years old or those with a family history of the disease. Rectal bleeding can be an early sign.
Angiodysplasia: A condition characterized by the presence of abnormal blood vessels in the colon, which can cause recurrent, painless rectal bleeding.
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 causing bowel obstruction and bleeding. It's rare in adults but more common in children.
Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause bleeding due to the presence of ectopic gastric mucosa.
Solitary Rectal Ulcer Syndrome: A condition characterized by the presence of 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 rectal bleeding in patients who have undergone pelvic radiation for cancer treatment.