Diverticulosis: This condition is a common cause of painless, bright red bleeding, especially in older adults. The presence of diverticula in the colon can lead to erosion of blood vessels, resulting in bleeding.

Hemorrhoids: Internal or external hemorrhoids can cause bleeding, especially during bowel movements. The bleeding is typically bright red and may be associated with pain or discomfort.
Anal Fissures: Tears in the lining of the anus can cause painful bleeding during or after bowel movements.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic inflammation and bleeding in the gastrointestinal tract.
Gastrointestinal Infections: Infections such as food poisoning or gastrointestinal viruses can cause inflammation and bleeding in the colon.

Colon Cancer: Although less common, colon cancer is a critical diagnosis to consider, as it can present with occult or overt blood in the stool. Early detection is crucial for effective treatment.
Angiodysplasia: Vascular malformations in the colon can cause bleeding, especially in older adults. This condition may not be immediately life-threatening but can lead to significant blood loss if not addressed.
Ischemic Colitis: Reduced blood flow to the colon can cause inflammation, bleeding, and potentially life-threatening complications if not promptly treated.

Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause bleeding due to the presence of ectopic gastric mucosa.
Intussusception: A condition where a part of the intestine telescopes into another, which can cause bowel obstruction and bleeding. It is rare in adults but more common in children.
Vascular Disorders: Conditions like hereditary hemorrhagic telangiectasia or blue rubber bleb nevus syndrome can cause vascular malformations leading to gastrointestinal bleeding.
Gastrointestinal Lymphoma: A type of cancer that can cause bleeding, although it is much less common than other causes of gastrointestinal bleeding.