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Blood in poo: Causes and diagnosis

Blood in poo may be discovered while wiping after going to the toilet or may be seen in the toilet bowl. Doctors may call this blood in stool or rectal bleeding.

Blood in poo is one of the symptoms the NHS has highlighted in its 'Be Clear on Cancer' campaigns, as it may be a sign of bowel cancer.

Although people are unlikely to talk about it, it is relatively common, affecting around 1 in 10 people in the UK.

There are several other possible reasons for seeing blood when using the toilet, but you should seek medical advice if you experience this so the cause can be diagnosed.

Causes of blood in poo

There may be tiny amounts of blood that can't be seen with the eye, or it may be obvious, sometimes looking like very dark like tar.

Whichever it is, it indicates bleeding somewhere in the digestive tract.

Possible causes of blood in poo include:

Piles (haemorrhoids). These swollen blood vessels in the rectal area can start bleeding, especially if poo is hard. Blood seen on toilet paper is likely to be streaky. Piles may feel itchy.

Anal fissure. This is a small and painful tear in the anal area. Blood from anal fissures is likely to be bright red. Pain and bleeding may continue after a bowel movement.

Anal fistula. This is a channel that forms between the anal canal (back passage) and near the anus. Anal fistulas can be painful, especially when going to the toilet.

Angiodysplasia. Painless rectal bleeding is caused by abnormal blood vessels in the gastrointestinal tract, and is more common in elderly people.

Gastroenteritis. This viral or bacterial stomach or bowel infection can cause diarrhoea with blood and mucus in it. Gastroenteritis is usually caused by food poisoning or the norovirus, for example, and may also cause stomach cramps and vomiting.

Diverticula. These are small bulges in the lower bowel's lining. There can be quite a lot of bleeding without pain if weaker blood vessels rupture with this condition.

Bowel cancer ( colon cancer, rectal cancer or colorectal cancer). The success of any cancer treatment often depends on early detection and treatment. As blood in poo is one of bowel cancer's early symptoms, it is not something to ignore.

Anticoagulant drugs ( blood thinners). A side-effect of these drugs, including warfarin or aspirin, is internal bleeding.

Inflammatory bowel disease(IBD) including Crohn's disease and ulcerative colitis. Blood in diarrhoea is a symptom of these long-term (chronic) digestive conditions that cause inflammation of the bowel lining.

Bowel polyps. These small growths on the lining of the colon or the rectum are common. They don’t always cause problems, but a small amount of blood when using the toilet possible.

Anal sex and sexually transmitted infections (STIs). Damage from anal sex or STIs may cause some rectal bleeding.

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