Faeces, abnormal

Faeces that differ from normal in colour, odour, consistency, or content. Abnormal faeces may indicate a disorder of the digestive system or related organ, such as the liver, but a change in the character of faeces is most often due to a change in diet. Diarrhoea may be due simply to anxiety or may be caused by an intestinal infection (see gastroenteritis); by an intestinal disorder such as ulcerative colitis or Crohn’s disease; or by irritable bowel syndrome. Loose stools may indicate malabsorption. Constipation is generally harmless but, if it develops unexpectedly, may be caused by a large-intestine disorder such as colon cancer. Pale faeces may be caused by diarrhoea, a lack of bile in the intestine as a result of bile duct obstruction, or a disease that causes malabsorption (such as coeliac disease). Such faeces may be oily, foul-smelling, and difficult to flush away. Dark faeces may result from taking iron tablets. However, if faeces are black, there may be bleeding in the upper digestive tract. Faeces containing excessive mucus are sometimes associated with constipation or irritable bowel syndrome. Enteritis, dysentery, or a tumour of the intestine (see intestine, tumours of) may result in excess mucus, which is often accompanied by blood. Blood in the faeces differs in appearance depending on the site of bleeding. Bleeding from the stomach or duodenum is usually passed in the form of black, tarry faeces. Blood from the colon is red and is usually passed at the same time as the faeces. Bleeding from the rectum or anus, which may be due to tumours or to haemorrhoids, is usually bright red. (See also rectal bleeding.)