Infectious Gastroenteritis: This is often the most common cause of bloody diarrhea, especially in children and young adults. It can be caused by a variety of pathogens including bacteria (e.g., Shigella, Salmonella, E. coli), viruses, and parasites. The presence of blood in the stool is usually due to the invasion of the intestinal mucosa by the pathogen.

Inflammatory Bowel Disease (IBD): Conditions like Ulcerative Colitis and Crohn's Disease can cause chronic bloody diarrhea due to inflammation and ulceration of the intestinal lining.
Food Poisoning: Certain types of food poisoning, such as that caused by E. coli O157:H7, can lead to bloody diarrhea.
Diverticulitis: Inflammation of a diverticulum in the wall of the colon can cause bloody diarrhea, although it more commonly presents with pain and changes in bowel habits.

Intussusception: A condition where a part of the intestine telescopes into another part, which can cause bloody diarrhea, especially in children. It's a medical emergency if not promptly treated.
Ischemic Colitis: Reduced blood flow to the colon can cause bloody diarrhea, and it requires immediate medical attention to prevent tissue death.
Clostridioides difficile (C. diff) Infection: While more commonly associated with non-bloody diarrhea, C. diff can cause bloody stools, especially in severe cases. It's crucial to diagnose and treat promptly due to its potential for severe complications.

Colonic Angiodysplasia: Vascular malformations in the colon can cause recurrent episodes of bloody diarrhea, more commonly in the elderly.
Colorectal Cancer: Although rare as a cause of acute bloody diarrhea, it should be considered, especially in older adults with a change in bowel habits or other alarming symptoms.
Hemolytic Uremic Syndrome (HUS): A complication of certain bacterial infections (like E. coli O157:H7) that can lead to bloody diarrhea, renal failure, and hemolytic anemia. It's more common in children but can occur in adults.