Here’s the thing about blood in your poop: It’s really hard to self-diagnose what’s causing it.

This is why Gail Bongiovanni, M.D., a gastroenterologist and adjunct professor in the division of digestive diseases at University of Cincinnati College of Medicine, told Self Magazine, it’s good to have some idea of what you might be dealing with. Here are the most common reasons you might see blood before you flush.

You Have Hemorrhoids.

Around three out of four adults will deal with these piles of swollen anal or rectal veins at some point in their lives, according to the Mayo Clinic. You can get them when you strain too much when trying to poop. Pregnancy, which causes constipation and increases pressure on your lower body (including your anus), is another main cause.

Sometimes you won’t even realize you have hemorrhoids, but straining to poop—and the resulting irritation—can make a hemorrhoid bleed, according to the Mayo Clinic. This blood will typically be bright red. Since hemorrhoids form on or close to your anus, blood doesn’t have time to clot up and darken before it exits the premises, Ashkan Farhadi, M.D., a gastroenterologist at MemorialCare Orange Coast Medical Center and director of MemorialCare Medical Group’s Digestive Disease Project in Fountain Valley, Calif., tells Self.

Hemorrhoids usually clear up on their own, but they can stick around and cause persistent bleeding, Dr. Farhadi says.

If hemorrhoids are indeed your issue, Dr. Farhadi recommends eating high-fiber foods to try to soften up your waste so pooping won’t require Herculean effort. (Be sure to also drink enough water, since the fiber soaks it up to help make poop softer and easier to pass.)

You Have an Anal Fissure.

Your anus is lined with thin, moist tissue known as mucosa, and when you get a small tear in that mucosa, it’s known as an anal fissure. You usually get an anal fissure when you expel an extraordinarily hard or large poop, according to the Mayo Clinic. As you can imagine, that can cause pain and bleeding. Just like with hemorrhoids, the anal fissure-induced blood you’ll see on your TP or in the toilet will likely be bright red.

Christine Lee, M.D., a gastroenterologist at Cleveland Clinic, likens anal fissures to having a papercut on your butt. Luckily, they usually get better on their own, though you can ask a doctor which anesthetic-containing cream they recommend to dull the pain in the meantime.

You Have a Peptic Ulcer.

A peptic ulcer is an open sore that develops either on the inside lining of your stomach (gastric ulcer) or the upper portion of your small intestine (duodenal ulcer), per the Mayo Clinic. These ulcers can happen due to bacterial infections and long-term use of painkillers like aspirin, ibuprofen, and naproxen sodium.

While the majority of people with peptic ulcers have no symptoms, the most common symptom you might experience is abdominal pain, the Mayo Clinic says. However, in less common and more severe cases, you can also end up with dark blood in your poop. “It can look like driveway tar—it’s shiny and sticky and has a peculiar odor to it,” Dr. Bongiovanni says.

If you have one of these ulcers, doctors may prescribe drugs to neutralize irritating stomach acid or medications to help protect the tissues that line your stomach and small intestine, the Mayo Clinic says. In some rare cases, you may need surgery to control the bleeding.

It Could be a Symptom of Crohn’s Disease or Ulcerative Colitis.

These are two different forms of inflammatory bowel disease. Both can cause chronic inflammation in your digestive tract that leads to bleeding ulcers, hence blood in your poop.

IBD treatment courses can vary wildly from person to person, but they can involve taking anti-inflammatory drugs like corticosteroids to tame inflammation, immunosuppressants to stop your immune system from attacking your digestive tract, and medicine to combat symptoms like diarrhea and constipation, according to the Mayo Clinic. Your doctor may also recommend surgery if other treatments haven’t helped as much as they should.

You Have a Polyp on Your Colon.

A polyp is a small mass of cells that can form on the lining of your colon, aka your large intestine, per the Mayo Clinic. Most of these polyps are harmless, but a small portion of them can develop into colon cancer over time.

It’s normal to have a colon polyp without symptoms, but if it becomes irritated, it can cause rectal bleeding and red or black poop, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Doctors treat colon polyps by surgically removing them, then making sure they’re not cancerous, says the NIDDK.

In Rarer Cases, Blood in Your Poop Could be a Sign of Colorectal Cancer.

Bright red rectal bleeding can sometimes be due to colorectal cancer, according to the American Cancer Society. Colorectal cancer is tough to pin down—it may not cause symptoms right away, the American Cancer Society says, and when it does, rectal bleeding can show up alone or with other issues. You might also experience things like diarrhea, constipation, a persistent urge to poop, abdominal pain, weakness and fatigue, and unintended weight loss.

One more thing: If your poop is black, that’s a big red flag that could signal internal bleeding, Dr. Bongiovanni says. That said, eating things like black licorice, blueberries, or beets can make this happen (so can taking iron supplements or medicines with Pepto-Bismol, per the U.S. National Library of Medicine. So, rule of thumb: If your poop is black and you didn’t recently have any of these foods or drugs, get to a doctor ASAP, just in case.