6 Medical Conditions That Cause Bloody Diarrhea

Any unexplained bleeding is worth getting checked out.

Unless you'd eaten beets earlier in the day, seeing red in the toilet bowl can be alarming. Bloody stool, also known as rectal bleeding, can be a symptom of many medical conditions, some relatively benign and some very harmful.

Depending on what's causing your bloody diarrhea, you might see blood in the toilet bowl, covering your poop, or only on the toilet paper after you wipe. It might be bright red, dark red, or even a super dark, tar-like color. The longer the blood sits inside your digestive tract, the darker it'll be since it spends a more prolonged time interacting with digestive chemicals. 

That means that, usually, bright red blood is less likely to indicate something serious because it usually starts low in your colon or rectum. However, seeing dark red blood in your diarrhea possibly means bleeding higher up in your digestive tract and needing to get checked out.

Regardless of the color of the blood in your diarrhea, Rabia De Latour, MD, an assistant professor in the department of medicine at NYU Grossman School of Medicine in New York, urged anyone who sees blood in their stool to see a doctor. 

"As a gastroenterologist, if you see someone with new rectal bleeding, especially if it's more than a few drops on the tissue or comes with a really painful bowel movement, you're doing a colonoscopy," Dr. De Latour told Health.

Here's what you need to know about six medical conditions that may cause bloody diarrhea. 


Hemorrhoids are one of the most common reasons you'll see blood in your stool; luckily, they're benign. Hemorrhoids are a normal cluster of blood vessels at the bottom of your rectum. 

"Everyone has them," Lisa Ganjhu, DO, a gastroenterologist at NYU Langone, told Health. What we think of as hemorrhoids are actually inflamed hemorrhoids, but the blood vessels are always there, inflamed or not.

Many people with hemorrhoids notice a small amount of bright red blood on the stool, toilet, or toilet tissue after a bowel movement.  

A flared hemorrhoid is full of blood, Dr. Ganjhu explained. Usually, the blood you see from hemorrhoids is bright red, and it coats your poop rather than mixing with it in the toilet bowl, added Dr. De Latour. 

And sometimes, when you have to strain really hard or poop a lot because of diarrhea, it can tear and cause bleeding. Usually, bleeding from hemorrhoids will resolve itself. 

"It's a vein, not an artery," explained Dr. De Latour. "So hemorrhoids tend to stop bleeding on their own." 

Dr. De Latour added that bad cases of hemorrhoids that continuously bleed are rare. Dr. De Latour suggested getting checked out if you haven't seen a healthcare provider about your hemorrhoids and noticed bleeding. 

You can help prevent hemorrhoids by doing the following:

  • Eat high-fiber foods
  • Use a stool softener or a fiber supplement
  • Drink enough fluids
  • Avoid straining during bowel movements
  • Avoid sitting on the toilet for long periods of time

Anal Fissures

Anal fissures are minor cuts that happen at the anus. 

"It's kind of like when you open your mouth really wide, and you get little tears at the corners," explained Dr. Ganjhu. 

When you get cracks near the corners of your mouth, usually there's some pain and some bleeding. And the same thing happens with anal fissures. 

"If you have a tear in your anus, that's painful," Dr. De Latour said. "It's not like the rectum where you don't have as much sensation—it's like skin almost." 

In fact, the main noticeable difference between having bleeding hemorrhoids (which happen in the rectum) and an anal fissure is the pain. If pooping is painful and you see blood, you probably have an anal fissure.

Anal fissures can happen for several reasons. Usually, they're seen after chronic constipation or straining. You push so hard to get stool out that you end up tearing the skin at your anus. But anal fissures also happen with chronic diarrhea and after childbirth. 

Anal fissures will likely bleed bright red, and you might see blood on the tissue or in the bowl, depending on how big the tear is or where it is.

"It might be a lot of blood if it's over a vein," noted Dr. Ganjhu. Again, any time you see blood, even if there's a good chance it's from a cut that will heal, it's a good idea to see your healthcare provider.

You can help prevent anal fissures by:

  • Avoiding hard bowel movements 
  • Increasing fiber in the diet
  • Using laxatives for hard stool

Inflammatory Bowel Disease (IBD)

Bloody diarrhea is often a symptom of Inflammatory Bowel Disease (IBD), an umbrella term for disorders that cause chronic inflammation in your digestive tract. Although, Dr. De Latour explained that bleeding is more familiar with ulcerative colitis (UC) than Crohn's disease, the two primary conditions under IBD.

Inflammation in the colon can cause ulcers, especially with UC. Bleeding from UC can be bright red or darker red since ulcers form in the rectum and large intestine or higher up in the gastrointestinal (GI) system. Those ulcers can then cause bloody stool.

IBD, in general, can cause bloody diarrhea when you have a flare-up because you're shedding inflammatory tissue. 

"With controlled inflammatory bowel disease or Crohn's disease, everything is normal," said Dr. Ganjhu. "But if there's a flare where there's a lot of inflammation and irritation, that's when you'll get diarrhea and the sloughing of all the tissue." 

You might see extra mucus and blood during those attacks, but that's nothing to be concerned about. If you haven't yet been diagnosed with IBD—Crohn's disease or UC—seeing blood in your stool is a significant signal to see your healthcare provider.

Another type of inflammation that can cause rectal bleeding is proctitis (inflammation of the rectum). Proctitis may be part of IBD and can be caused by certain infections, such as sexually transmitted infections (STIs) or food poisoning. In addition, radiation proctitis can occur after a person receives radiation therapy to treat cancer.

The mechanisms by which IBD occurs remain elusive. Although you cannot prevent IBD, there are some steps you can take to prevent or minimize flare-ups, such as:

  • Not smoking
  • Staying up-to-date on vaccinations (some infections may worsen your symptoms)
  • Screening for colorectal and cervical cancers
  • Consulting your healthcare provider about depression or anxiety
  • Checking your bone density (IBD may increase your risk of developing osteoporosis)


"E. coli and other bacteria cause an invasive infection, so you get the inflammation and sloughing of tissues like with IBD that leads to bloody diarrhea," said Dr. Ganjhu.

Infections that may cause bloody stool include:

  • GI infections: The most common types of GI infections that cause rectal bleeding include infectious colitis or food poisoning.
  • Diverticulitis: Another type of infection occurs when diverticula (bulges of tissue in the colon's wall) form and become inflamed. According to Dr. De Latour, they're "almost like wrinkles" that form from increased pressure inside the colon that causes the colon wall to weaken. If a person has significant bleeding from diverticulitis, they'll sometimes need surgery to keep it from happening again.
  • STIs: Gonorrhea, chlamydia, herpes, and syphilis are the most common STIs that cause rectal bleeding.

You can prevent GI infections by practicing good hygiene. And you can minimize your risk of contracting STIs by practicing safe sex and using condoms during sex (including oral, anal, and vaginal sex).

As for diverticulitis, the mechanisms by which the infection occurs remain unknown, so healthcare providers cannot prevent it.

Colorectal Cancer

One of the most feared causes of bloody diarrhea is colorectal cancer

Although people previously believed colorectal cancer only happens in mid-life, healthcare providers now see younger and younger people receive diagnoses. And the rise of colorectal cancer among young people is a significant reason you should see a doctor if you notice blood in your stool. It's best to rule out cancer rather than wait to see if the bleeding worsens.

"When you have adults who have unexplained rectal bleeding, especially if it's associated with weight loss or if they have a family history of colon cancer or any other concerning symptoms, they should see a gastroenterologist because it could be cancer," explained Dr. De Latour.

Colorectal cancer can cause bloody diarrhea or stool when the tumors leak blood. The whole purpose of tumors is to keep growing; to do so, they tap into your blood supply to suck up all the nutrition. 

"So tumors tend to be very vascular, very bloody," said Dr. De Latour. 

When they're sitting inside your digestive tract, they can leak blood that you might see inside your toilet bowl, or that might make your poop look darker than usual. If you're noticing dark brown or black stool or bright red blood on your tissue paper, it might be a symptom of colorectal cancer.

You should talk to your healthcare provider about being routinely screened for colorectal cancer, starting at age 45. Early screenings can help detect precancerous polyps before cancer progresses.

Other steps that you can take to lower your risk of developing colorectal cancer include:

  • Incorporating a healthy diet that decreases the number of animal fats and increases the number of fruits, vegetables, and whole grains
  • Taking low-dose of aspirin (although research is limited regarding the association between aspirin and the risk of developing cancer)
  • Being physically active
  • Maintaining a healthy body weight
  • Decreasing alcohol consumption
  • Not smoking


Ulcers are sores that are slow to heal or keep returning. And like UC, ulcers that form as a result of other disorders can cause bloody diarrhea. However, these types of ulcers are rare.

"It's called solitary rectal ulcer syndrome (SRUS). You get these big ulcers in the colon, especially in the rectum," explained Dr. De Latour. 

In addition to rectal bleeding, research suggests that symptoms of SRUS most commonly include:

  • Mucus discharge from the rectum
  • Excessively straining for long periods of time
  • Pain in the perineal and abdominal regions
  • Feeling incomplete after having a bowel movement
  • Constipation
  • Rarely, rectal prolapse (which happens when the large intestine partly slips out through the anus)

Healthcare providers typically see SRUS in older people with limited mobility, added Dr. Ganjhu. When an older person cannot get to the bathroom on their own or aren't able to tell someone when they need to go to the toilet, their stool sits in the rectum and causes a pressure ulcer. 

Ulcers can also happen when an older person falls or if they don't move very often.

A Quick Review

Blood in the stool may be due to several causes—including inflammation, infection, hemorrhoids, anal fissures, ulcers, or colorectal cancers.

Fortunately, most of those causes of rectal bleeding are not life-threatening. Still, if you notice blood in the stool, consult your healthcare provider.

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