Colorectal Cancer Association of Canada - CCAC

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Black poo? THREE reasons for strange bowel symptom - and if you should see doctor

BLACK POO is unusual and often down to diet changes, but it could also be a sign of bowel cancer and internal bleeding.


Black poo is one of a number of shades your stools can turn, and it could indicate diet or a medical condition.

It is worth paying attention to poo colour since it can often be a good indicator of health.

According to the Mayo Clinic, all shades of brown - and even green - are considered normal.

However, dark red poo can indicate bowel cancer, while white or clay-coloured stools may point to diseases of the liver or bile ducts.

Black poo may be triggered by bleeding in the upper digestive tract, such as the oesophagus and stomach.

In these cases blood is digested for longer than if bleeding was taking place in the bowel and around the anus which would leave the stool a red colour instead.

Bleeding in any of these parts of the gastrointestinal tract could be very dangerous and you should see a doctor as soon as possible.

This is because bleeding could be potentially caused by an ulcer or tumour, and may prove fatal.

Bowel cancer

According to Cancer Research UK, dark or black-coloured stools could indicate cancer higher up in the bowel - known as the colon.

Bowel cancer is the second most common cause cancer death in the UK.

Black poo may be accompanied by other symptoms, including a change in bowel habits - like diarrhoea and constipation - as well as rectal bleeding.


This is inflammation of the stomach lining and could be caused by over-indulging in alcohol, spicy foods and smoking.

It could also be triggered by over-use of NSAIDs and a bacterial infection.

The condition could be caused by black or dark-coloured stools due to bleeding.

If left untreated, it could lead to dangerous loss of the stomach lining and glands.

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