What are the causes of black stool?

The intestines and colon are responsible for digesting nutrients from food and then passing the rest of it from the body as waste. This material that forms in the colon is called a stool. Sometimes it can be loose, as in the case of diarrhoea, and other times it can be impacted and hard to pass, as in the case of constipation. In either situation, there are times when the stool can become black for several reasons.


Gastritis is a condition characterised by an inflammation of the stomach lining. It can be either chronic, which means it takes place over time, or it can be acute, where it happens all of a sudden. In either case, in can be caused from excessive alcohol intake, using too many pain-relieving medications or the result of severe stress. Some of the symptoms include bloating, vomiting and dark stools.


As people age, they sometimes develop small pouches on the walls of their intestines called diverticula. When these pouches appear, they often do not come with any symptoms, and this condition is called diverticulosis. When these diverticula become infected and inflamed, the condition gets changed to diverticulitis. Symptoms of diverticulitis include constipation, abdominal pain and black stools.


Ulcerative colitis is a type of inflammatory bowel disease that causes the large intestine to become swollen. This condition is characterised by abdominal pain, diarrhoea and black stools. Another form of inflammatory bowel disease that can cause black stools is called Crohn's disease. This condition is similar to colitis in that it causes inflammation, but it is not localised to a specific area. It can occur anywhere along the digestive tract, from the mouth all the way to the rectum.


There are two types of ulcers that can occur in the stomach: peptic ulcers and gastric ulcers. In peptic ulcers, the lining of the stomach and the first part of the small intestine, called the duodenum, become eroded. When there is an actual break in the lining of the stomach, a gastric ulcer results. In both of these conditions, nausea, abdominal pains and dark, tarry stools can be present.


There are various supplements and foods that can make stools dark. Iron pills and supplements, for example, are used when iron levels are low in the body, and they can cause stools to appear dark. Bismuth medicines, such as Pepto Bismol, lead and black liquorice, can turn stools dark. Blueberries can also lead to dark stools.

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