What Causes Bloody Diarrhea? These 6 Medical Conditions Are Common Culprits

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 of them 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, and it might be bright red or dark red or even a super dark, tar-like color, according to the Cleveland Clinic. The longer the blood sits inside your digestive tract, the darker it'll be since it spends a longer 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. Seeing dark red blood in your diarrhea, however, likely means you're bleeding higher up in your digestive tract and need to get checked out.

Regardless of the color of the blood in your diarrhea, Rabia De Latour, MD, a gastroenterologist at NYU Langone, urges 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," she tells Health.

Read on for six of the most common causes of bloody diarrhea.


Hemorrhoids are one of the most common reasons you'll see blood in your stool and, 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, tells Health. What we think of as hemorrhoids are actually inflamed hemorrhoids, but the blood vessels are always there, inflamed or not.

A flared hemorrhoid is full of blood, Dr. Ganjhu explains. And sometimes, when you have to strain really hard or when you're pooping a lot because of diarrhea, it can tear and cause bleeding. Usually, the blood you see from hemorrhoids is bright red, and it coats your poop rather than mixing with it in the toilet bowl, says Dr. De Latour.

Usually, bleeding from a hemorrhoid will resolve itself. "It's a vein, not an artery," says Dr. De Latour. "So hemorrhoids tend to stop bleeding on their own." However, she has seen bad cases that continuously bleed, though that's rare. If you haven't yet seen a doctor about your hemorrhoids and you notice bleeding, Dr. De Latour suggests getting checked out.

Anal fissures

Fissures are small 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," Dr. Ganjhu says. When that happens, usually there's some pain and some bleeding. The same thing happens with anal fissures. "If you have a tear in your anus, that's painful," Dr. De Latour says. "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 a bleeding hemorrhoid (which happen in the rectum) and an anal fissure is the pain, she says. If pooping is painful and you see blood, you probably have a fissure.

Anal fissures can happen for several reasons. Usually they're seen after chronic constipation or straining, per the Cleveland Clinic. 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. 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, Dr. Ganjhu says. "It might be a lot of blood if it's over a vein," she says. Again, any time you see blood, even if there's a good chance it's from a cut that will heal itself, it's a good idea to see your doctor.


Bloody diarrhea is often a symptom of Inflammatory Bowel Disease (IBD), which is an umbrella term for disorders that cause chronic inflammation in your digestive tract. Bleeding is more common with ulcerative colitis than Crohn's disease (the two main disorders under IBD), Dr. De Latour says. Inflammation in the colon can cause ulcerations, especially with ulcerative colitis, and those ulcers can then cause bloody stool, she says. Bleeding from ulcerative colitis can be either bright red or darker red because ulcers may form in the rectum and large intestine or higher up in the gastrointestinal (GI) system, according to Crohn's and Colitis Canada.

IBD, in general, can cause blood in your diarrhea when you have a flare because you're shedding inflammatory tissue, Dr. Ganjhu says. "With controlled inflammatory bowel disease or Crohn's disease, everything is normal," she says. "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." During these attacks, you might see extra mucus as well as blood, but that's nothing to be concerned about, according to Crohn's and Colitis Canada. If you haven't yet been diagnosed with IBD—Crohn's or ulcerative colitis—seeing blood in your stool is a major signal to see your doctor.


Some GI infections can lead to bloody diarrhea, such as infectious colitis or even food poisoning, Dr. Ganjhu says. "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," she says.

One such infection is called diverticulitis, which is pretty common, Dr. De Latour says. Diverticulitis is the infection and inflammation of diverticula, which are bulges of tissue in the wall of your colon. "They're almost like wrinkles," notes Dr. De Latour. Really, they form from an increase in pressure inside the colon that causes the colon wall to weaken and diverticula to form. "Usually, they don't cause problems for people but if one of those bulges erupts into a vessel, it can cause pretty significant chronic bleeding," Dr. De Latour says. If a patient has enough bleeds from diverticulitis, they'll sometimes need surgery to keep it from happening again.

Colorectal cancer

The most feared cause of bloody diarrhea is cancer, specifically colorectal cancers, Dr. De Latour says. Although colorectal cancers were once thought to only happen in mid-life, doctors are now seeing younger and younger people diagnosed. The rise of colon and rectal cancers among young people is a major reason she urges anyone who sees blood in their stool to see a doctor—it's best to rule cancer out rather than wait to see if the bleeding gets worse.

"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," she says.

Colorectal cancers can cause bloody diarrhea or bloody stool when the tumors leak blood. Tumors are like evil geniuses, Dr. De Latour says. Their whole purpose is to keep growing and, to do so, they tap into your blood supply to suck up all the nutrition. "So tumors tend to be very vascular, very bloody," Dr. De Latour says. 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 and/or bright red blood on your tissue paper, it might be a symptom of colorectal cancer.


Like with ulcerative colitis, ulcers from other disorders can cause bloody diarrhea. However, these types of ulcers are rare, Dr. De Latooour says. "It's called solitary rectal ulcer syndrome (SRUS). You get these big ulcers in the colon, especially in the rectum."

SRUS is typically seen in much older people who have limited mobility, Dr. Ganjhu says. When an older person can't get to the bathroom on their own and aren't able to tell someone when they need to go to the bathroom, their stool can just sit in the rectum and cause a pressure ulcer, she says. Ulcers can also happen when an older person falls or if they don't move very often.

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