What should you know about dark foul smelling stool?

Dark stool may follow dark foods, iron, or some medicines, and strong odour can occur after a temporary dietary change or altered digestion. Black, sticky, tar-like stool is different: it can indicate bleeding higher in the digestive tract and should not be dismissed. Very pale stool with dark urine or yellow skin may suggest reduced bile flow or a liver-related condition. Smell and colour alone cannot establish a diagnosis, so describe the change carefully.

Think back to recent meals, iron products, bismuth-containing medicines, antibiotics, travel, and changes in bowel frequency. Keep hydrated, especially if stools are loose, unless a clinician has advised fluid restriction. Do not stop prescribed treatment without advice. Arrange a review if the change persists, keeps returning, or occurs with abdominal discomfort, diarrhoea, weight loss, or unusual tiredness. A clinician may ask about the stool and examine or test you.

Seek urgent medical care for black tarry stool, fresh blood, vomiting blood, severe abdominal pain, fainting, confusion, or marked weakness. Prompt advice is also needed with persistent vomiting, fever, signs of dehydration, or yellow eyes and skin. Do not wait for a dietary explanation if you feel acutely unwell.

Ask whether the colour could be caused by a medicine or supplement and whether stool or blood testing is needed. Tell the clinician when it started, how often it occurs, its texture, recent foods, bowel symptoms, pain, dizziness, and any dark urine or yellowing.