Black and loose stool: possible causes and warning signs

Loose stool can happen when the bowel moves contents quickly, including during an infection or after a food change. Black stool may instead result from iron, bismuth, or strongly coloured foods. When blood is digested before passing through the bowel, it may look black and tar-like. Gastritis, Helicobacter Pylori Infection, and Peptic Ulcer can involve the upper digestive tract and may present with black stool. Loose consistency does not make black stool automatically harmless.

Pay attention to whether the bowel movement is sticky, has an unusually strong smell, or is accompanied by cramps, fever, nausea, vomiting, pallor, or light-headedness. A clinician can help separate a colour change from bleeding.

Write down what you ate and which medicines or supplements you used before the change. Drink small, frequent amounts of fluid if you can keep them down, and choose simple foods while loose stools continue. Avoid taking anti-diarrhoeal medicine when stool is black or when you have fever, severe pain, or suspected bleeding unless a clinician advises it. Contact a healthcare professional promptly if the colour is unexplained or continues.

Go to urgent care if black loose stool occurs with fainting, severe weakness, confusion, breathlessness, a fast heartbeat, severe abdominal pain, repeated vomiting, blood in vomit, or coffee-ground-like vomit. Also seek prompt help if you cannot drink, are passing very little urine, or the stool keeps returning. These features may indicate bleeding or significant dehydration.

Ask whether a medicine, supplement, food, infection, or digestive condition could explain the change. Tell the clinician when it started, how many bowel movements you have had, whether they are tarry, and whether pain, fever, vomiting, dizziness, or reduced urination is present. Ask whether Gastritis, Helicobacter Pylori Infection, or Peptic Ulcer needs evaluation.