"Identifying When Blood in Your Stool May Indicate Colorectal Cancer"

Spotting blood in the toilet after you use the bathroom can be a jarring experience. Though some may be tempted to ignore the issue, experts warn that this symptom deserves a second look.

In the U.S., colorectal cancer is the fourth most commonly diagnosed cancer, and rates have been on the rise for decades, particularly for people under the age of 45.

Rectal bleeding, also known as hematochezia, is a symptom commonly seen in colorectal cancer patients, said Jingquan (Caron) Jia, MD, PhD, a clinical associate professor in the division of medical oncology at the University of North Carolina at Chapel Hill School of Medicine.

This is especially true in younger patients, she told Health. In fact, new research published in May dubbed blood in stool one of two “red flag” symptoms of early-onset colorectal cancer.

However, not all rectal bleeding is a sign of colorectal cancer—in some cases, the blood in your stool can be caused by hemorrhoids, a hard bowel movement, or other more benign causes.

“Many of the reasons behind rectal bleeding have nothing to do with colon cancer and are completely benign things,” Felice Schnoll-Sussman, MD, a gastroenterologist at Weill Cornell Medicine, told Health. “But most cases of colon cancer do have some blood at times.”

So what should you make of rectal bleeding when you see it, and how can you determine if it’s a sign of cancer or another serious condition? Here’s what experts had to say.

Most basically, hematochezia is what happens when a person passes blood through their gastrointestinal tract, said Schnoll-Sussman.

That blood can appear within the stool itself, or people might see it in the toilet or on toilet paper. It can also look quite different—some people may notice bright red blood, while others may have melena, or black, tarry stool, she added.

Though not all colorectal cancers cause rectal bleeding, it is a common symptom. That blood in the stool that people see can be caused by a polyp—a precancerous growth—or a tumor, said Jatin Roper, MD, an assistant professor of medicine in the division of gastroenterology at the Duke University School of Medicine.

“One hallmark of these cancers is that they have a lot of blood vessels,” he told Health. “So as a polyp grows into a larger polyp, and from a larger polyp into cancer, those blood vessels grow more extensively.”

These blood vessels can irritate and grow into the colon’s lining, Schnoll-Sussman added, and as stool passes through the gastrointestinal tract, it can rupture them. The blood vessels may also spontaneously start bleeding as the tumor grows larger and cells break off, Zuri Murrell, MD, a colorectal surgeon at Cedars-Sinai Cancer in Los Angeles, told Health.

“These cancer cells grow, grow, grow, outgrow their blood supply, literally break off, but the blood vessels are still there, shooting blood into the colon, for lack of a better term,” he explained.

Because the blood is coming directly from the tumor itself, the severity or amount of blood in stool is related to how advanced the cancer is, said Roper.

However, any bleeding associated with colorectal cancer is normally quite noticeable, said Jia.

“It is more than just [seeing] a little bit of pink tinge on the toilet tissue,” she said. “Some patients even notice blood clots.”

The actual look of the rectal bleeding in association with colorectal cancer can vary pretty dramatically, largely depending on where the cancer itself is located in the body.

“If a cancer is on the left side of the colon, meaning it’s closer to the anus, the blood is more likely to be red blood mixed with regular stool,” Roper explained.

However, if the blood is coming from a tumor further up in the colon on the right side, he said, that blood has likely been partially digested in some way, he added.

Depending on how far that blood had to travel through the gastrointestinal tract, it might be melena (a black stool), or it might be maroon in color, said Roper.

Though it’s important that doctors and patients consider colorectal cancer if they’re seeing rectal bleeding, there are many other potential causes of hematochezia.

In some cases, like colorectal cancer, rectal bleeding is a sign of something very serious.

One possible driver is gastrointestinal bleeding, which could come from the stomach or the intestine, said Roper. This bleeding could be caused by an ulcer, for example, or by diverticular bleeding, a condition where pouches of the colon (called diverticula) spontaneously start bleeding, he explained. Diverticular bleeding is the most common cause of rectal bleeding in older people, Roper added.

“If not investigated and not evaluated in a hospital setting, that can be life-threatening,” he explained.

Blood in the stool can also indicate that someone has inflammatory bowel disease, Crohn’s disease, or ulcerative colitis.

But in many cases, rectal bleeding—especially bright red blood mixed in with stool—is caused by hemorrhoids, Murrell explained. These can be either internal or external.

“External hemorrhoids hurt. Internal hemorrhoids are painless, but they can bleed and cause itching,” he said.

Rectal bleeding can also be associated with lesser-known conditions that need treatment but aren’t necessarily emergencies. These include anal fissures, a painful “cut over the sphincter muscle,” Murrell said, as well as an anal abscess, which swells and is painful to the touch. A third possibility is a fistula, or an abnormal connection between the skin and the anus, which can sometimes bleed, Murrell explained.

Some people may even see small amounts of blood after a particularly hard bowel movement, Murrell explained. So long as this resolves within a day or so, there should be no cause for concern.

Often mistaken for hematochezia, sometimes stool can even appear maroon once because of a person’s diet—Murrell has seen this in some of his patients who’ve eaten large amounts of beets, blackberries, or blueberries, for example.

Though the type or amount of blood a person sees in their stool can give some clues as to what’s going on, there’s no obvious way for a person to tell whether their rectal bleeding is cancer-related just by looking at it.

“The frequency and the amount of bleeding can vary,” said Jia. “So I don’t think any single factor would reliably point towards [colorectal cancer] one way or the other.”

However, often, people will have rectal bleeding in association with other colorectal cancer symptoms, such as abdominal pain, changes in bowel habits, or fatigue, Murrell explained. If it’s rectal bleeding plus something else, that could be a sign that something more serious is going on.

Cancer-related bleeding is also persistent, Jia added—it won’t simply go away.

“After treating for a hemorrhoid for a month or two, or even longer, if that patient’s symptoms [do] not improve, that should really raise a red flag,” said Jia.

Experts agree any rectal bleeding is a cause for concern and should be evaluated by a doctor.

If someone is seeing a lot of blood and is experiencing other symptoms such as chest pain or shortness of breath, “that’s an emergency, potentially, and that might be indicative that the person is bleeding so much that their blood pressure is going down, and that they’re not supplying enough blood to their brain or their heart,” said Schnoll-Sussman. If this is the case, someone should see a healthcare provider immediately.

If the hematochezia doesn’t seem like an emergency but continues to last for a few days, you should try to schedule an appointment with a doctor as soon as possible.

“If you notice that every time you have a bowel movement,” Murrell explained, “and you see blood every single time—whether your stool is hard or soft—you need to be evaluated.”

When discussing rectal bleeding with their doctor, there is a risk that someone could get misdiagnosed, especially if they’re younger, said Jia. This is simply because hematochezia as a symptom is so nonspecific.

“I can’t tell you how many patients I’ve had who’ve gone to an urgent care or an ER, and they’ll just say, ‘Hey, doc, I got bright red blood.’ And they’ll just give them a cortisone cream or something without even doing a rectal exam,” said Murrell. “[Patients] have to be their own healthcare advocate…If it’s not better, then you have to go back.”

These statistics about the rising incidence of early-onset colorectal cancer are also a good reminder for people to remember the importance of screening tests and colonoscopies. Because not all cases of colorectal cancer cause obvious bleeding, people can take screening tests that look for blood in the stool that’s not visible to the naked eye, Schnoll-Sussman said, or they can use tests that check for some other marker of colorectal cancer.

In general, rectal bleeding can be scary, Schnoll-Sussman said, and it’s always easier to assume that the symptom is nothing or the issue will pass. And talking about rectal bleeding with a doctor can also feel embarrassing, she added. However, delaying care is never the answer.

“You shouldn’t die from fear, and you shouldn’t die from embarrassment,” said Murrell. “If you catch [colorectal cancer] early, it is curable by surgery. It is literally curable. So don’t become the self-fulfilling prophecy, because if you’re embarrassed long enough and you’re scared long enough that this is not going to be curable, guess what? It won’t be.”