Normal variation in stool color: In infants, especially those who are breastfed, green diarrhea can be a normal variation due to the foremilk being rich in lactose, which can cause rapid transit through the gut, resulting in greenish stools.

Viral gastroenteritis: Common viruses like rotavirus, norovirus, and adenovirus can cause green diarrhea in infants due to the infection of the gastrointestinal tract.
Dietary factors: Introduction of new foods or drinks, or a change in the mother's diet if breastfeeding, can lead to changes in stool color, including green diarrhea.
Gastroesophageal reflux disease (GERD): Although not directly causing green diarrhea, GERD can lead to regurgitation and subsequent passage of bile-stained stools, which may appear green.

Intussusception: A condition where a part of the intestine slides into an adjacent part, which can cause bowel obstruction and ischemia. Early signs may include green vomiting or diarrhea, making it crucial not to miss this diagnosis.
Biliary atresia or other biliary tract abnormalities: Obstruction of the bile ducts can lead to pale stools, but in some cases, especially if there's partial obstruction, stools might appear green due to the presence of bile.
Infectious causes requiring specific treatment: Such as bacterial infections (e.g., Salmonella, Shigella) or parasitic infections, which can present with green diarrhea and require prompt and specific antimicrobial therapy.

Congenital intestinal anomalies: Conditions like intestinal malrotation or Hirschsprung's disease can lead to abnormal stool colors, including green, due to obstruction or altered gut motility.
Chromosomal disorders: Certain genetic conditions can affect the gastrointestinal system, leading to unusual stool colors among other symptoms.
Metabolic disorders: Some inborn errors of metabolism can result in gastrointestinal symptoms, including changes in stool color, though these are exceedingly rare and usually accompanied by other systemic signs.