Viral Gastroenteritis: This is often the most common cause of green stool diarrhea, especially in children and young adults. Viruses such as norovirus, rotavirus, and adenovirus can cause inflammation of the stomach and intestines, leading to diarrhea that may appear green due to the presence of bile.

Bacterial Gastroenteritis: Bacteria like Salmonella, Shigella, and Campylobacter can cause green stool diarrhea. These infections often result from consuming contaminated food or water.
Food Poisoning: Consuming spoiled or contaminated food can lead to green stool diarrhea. This is often due to the presence of toxins or bacteria in the food.
Irritable Bowel Syndrome (IBS): Although less common, some individuals with IBS may experience green stool diarrhea, particularly if they have a predominance of diarrhea over constipation.

Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic diarrhea, which may be green. Missing these diagnoses can lead to significant morbidity and potential complications if not treated properly.
Giardiasis: An infection caused by the Giardia parasite, which can lead to severe and prolonged diarrhea. It's crucial to diagnose and treat giardiasis to prevent malabsorption and weight loss.
Intestinal Obstruction: Although less common, an obstruction in the intestines can cause diarrhea, including green stool, due to the partial blockage of normal intestinal flow.

Malabsorption Syndromes: Conditions such as celiac disease or pancreatic insufficiency can lead to malabsorption of nutrients, resulting in diarrhea that may appear green due to the presence of undigested fats.
Whipple's Disease: A rare, systemic bacterial infection caused by Tropheryma whipplei, which can lead to malabsorption, weight loss, and diarrhea, among other symptoms.
Short Bowel Syndrome: A condition that results from a significant loss of intestinal tissue, leading to malabsorption and chronic diarrhea, which may be green in color.