Infectious Colitis: This is often the most common cause of diarrhea with bloody mucus, typically resulting from bacterial infections such as Shigella, Salmonella, or Campylobacter, or viral infections like Norovirus. The presence of blood and mucus in the stool is characteristic of an inflammatory process in the colon.

Inflammatory Bowel Disease (IBD): Conditions like Ulcerative Colitis and Crohn's Disease can cause chronic diarrhea with blood and mucus due to inflammation of the gastrointestinal tract.
Food Poisoning: Certain types of food poisoning, especially those caused by bacteria like E. coli, can lead to bloody diarrhea.
Diverticulitis: Inflammation of the diverticula in the colon can cause diarrhea with blood and mucus, especially in older adults.

Clostridioides difficile (C. diff) Infection: Although not always bloody, C. diff can cause severe diarrhea and is a critical diagnosis to consider, especially in patients with recent antibiotic use or healthcare exposure, due to its potential for severe complications.
Ischemic Colitis: Reduced blood flow to the colon can cause sudden onset of bloody diarrhea, which is a medical emergency requiring prompt diagnosis and treatment.

Intussusception: A condition where a part of the intestine slides into an adjacent part, which can cause intestinal obstruction and bloody stools, more common in children but can occur in adults.
Colonic Carcinoma: Although rare as a cause of acute diarrhea with blood and mucus, colorectal cancer can present with these symptoms, especially in older adults or those with risk factors.
Allergic Colitis: Seen primarily in infants, this condition is caused by an allergic reaction to milk protein, leading to bloody stools.
Eosinophilic Colitis: A rare condition characterized by eosinophilic infiltration of the colon, which can cause diarrhea, blood, and mucus in the stool, often associated with other allergic conditions.