Causes of Blood in Stools

The presence of blood in stools is a very frequent sign of different gastrointestinal diseases. Unfortunately, it can indicate the presence of malignant pathologies such as colorectal carcinoma.
Causes of Blood in Stools

Last update: 02 June, 2023

Blood in stools often causes great alarm in people who suffer from it. It shows that something isn’t working properly in the digestive tract. Are you interested in knowing what are the causes of blood in stools? Keep reading and we’ll tell you.

The gastrointestinal system is lined with mucous tissue supplied by a large number of blood vessels. Studies affirm that the causes of blood in the stool include the pathologies responsible for upper and lower digestive bleeding. In addition, this sign is usually one of the early manifestations of colorectal cancer.

Common causes of blood in stools

In most cases, the presence of blood in stools is the result of an injury to the intestinal lining or its vascular elements. Traumatic, inflammatory, and gastrolesive phenomena are directly related to this condition. Also, doctors often describe the presence of this symptom as hematochezia.

The color of the blood allows one to suspect the origin of the bleeding in the digestive tract. In this sense, bright red blood (rectal bleeding) is associated with colon and rectal disorders, while dark blood mixed with stool (melena) leads to esophagus, stomach, and small intestine disorders. Among the most common causes of blood in stools are the following.


Among the causes of blood in stool are fissures and hemorrhoids
In addition to the classic bleeding with the stool, hemorrhoids often cause pain that is not always related to defecation.

Hemorrhoids are the most common cause of bright red blood in stools. They’re the result of inflammation and dilation of the veins that surround the anal canal. In the same way, they’re usually accompanied by a sensation of rectal occupation, itching, and perianal discomfort. In some cases, these can cause thrombi and protrude as a palpable lump.

Research affirms that hemorrhoids have a prevalence of more than 50% in adults over 50 years of age. They are classified as internal and external according to their location with respect to the pectineal line of the rectal ampulla. In general, the external ones cause greater discomfort, while the internal ones tend to produce greater loss of blood in feces.

Anal fissure

An anal fissure is a cut or tear in the tissue that surrounds and lines the anus. Causes include overexertion when defecating, passing hard stools, ongoing bouts of diarrhea, and anal intercourse.

Blood is usually evidenced on toilet paper or straight into the toilet. In addition, the presence of pain during evacuation is frequent, and this can last for several hours.

In most cases, these lesions appear as a crack in the sphincter of the anus, accompanied by a small lump or fibroma, similar to protruding hemorrhoids. Anal fissures usually heal spontaneously; however, if pain and bleeding persist, or new symptoms appear, then it’ll be necessary to see a specialist doctor.

Inflammatory conditions

Inflammatory pathologies of the intestinal mucosa promote vasodilation, ulceration, and long-term blood loss. In this sense, ulcerative colitis and Crohn’s disease are some of the most common causes of blood in stools. In addition, affected people often have abdominal cramps, diarrhea, weight loss, fatigue, and decreased appetite.

Irritable bowel syndrome and diverticular disease are other inflammatory causes of bloody stools. In these conditions, the blood may be bright red or dark red depending on the severity of the injury and the location of the bleeding. Early diagnosis and therapeutic approach determine a better prognosis and quality of life.


Polyps are raised lesions of the lining of the digestive tract that protrude into the intestinal lumen. They’re generally benign and can vary in size and build. However, studies suggest that about 95% of advanced adenomatous polyps can progress to colorectal cancer.

In most cases, these lesions cause few symptoms. However, large polyposis can injure surrounding blood vessels and lead to blood loss in the stool. For this reason, all patients with an average risk should have early detection tests starting at the age of 45.


Constipation is usually associated with a decrease in the number of bowel movements and an increase in the consistency of the stool. Hard, dry stools can injure the mucosa and rectal sphincter, causing blood loss through the rectum. This fact promotes the appearance of small stains of bright red blood on the toilet paper.

Low fiber diets, not ingesting enough water per day, obesity and lack of exercise are determining factors for this condition. In this sense, people should seek medical help for any difficulty in defecating, especially if it’s accompanied by pain and bleeding.

Intestinal infections

Colonization and infection of the digestive tract by invasive microorganisms usually manifests itself through bloody diarrhea and abdominal discomfort. Escherichia coli, Shigella, and Entamoebahistolytica gastroenteritis are some of the most common causes of bloody stools and mucus. In addition, people often report vomiting, nausea, abdominal pain, and dehydration.


Generally, the inflammation and irritation of the rectum and anus are accompanied by symptoms such as pain, rectal urgency, a feeling of anal occupation, and bleeding. Some patients may be complicated by anemia, intestinal ulcers, and perianal fistulas. The causes of this condition range from infectious and inflammatory pathologies to radiation therapy for cancer.

Colon cancer

The detection of hidden blood in stools is usually one of the main diagnostic tools for colon cancer, especially in the early stages. On the other hand, evidence of bleeding to the naked eye during evacuation may be associated with more advanced stages of the disease.

However, the specialist doctor must first rule out other pathologies that are commonly associated with intestinal bleeding. In addition, the history of immediate family members who have had colon cancer, as well as personal medical history of polyps and other neoplastic conditions, should be taken into account.

Risk factors for blood in stools

The presence of blood in stools is associated with multiple causes related to the injury and rupture of the blood vessels that nourish the intestinal tissue. There are several factors that increase the probability of developing these diseases and of suffering from medium or long-term rectal bleeding, among which are the following:

  • Excessive straining or when defecating
  • Practicing anal sex
  • Having repeated diarrhea or constipation
  • Low-fiber diets
  • Sedentary lifestyle and obesity
  • Insufficient water intake per day
  • Smoking
  • Excessive alcohol consumption

When to see the doctor?

Causes of blood in stools can be resolved with medical treatment
There are several medical specialists who can treat a case of bleeding in the stools. Among them, gastroenterologists and coloproctologists.

Early detection of blood in the stools determines a better prognosis and short-term symptom relief. For this reason, it’s essential to seek medical attention as soon as possible if you have rectal bleeding accompanied by any of the following clinical manifestations:

  • Pain and discomfort when defecating
  • Changes in the consistency of stools
  • Unexplained weight loss
  • Fatigue and excessive tiredness
  • Incontinence or lack of control during defecation
  • Drowsiness and loss of consciousness

A symptom that something is wrong

The causes of blood in stools are very varied, with hemorrhoids and anal fissures being some of the most frequent. However, all uncontrolled bleeding implies a decrease in circulating blood volume with multiple systemic complications. In this sense, this condition is a red flag that can’t be underestimated and requires immediate professional medical attention.

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