"Blood in your stool typically means that you are bleeding from somewhere in your intestines," says Christian G. Stevoff, MD, a gastroenterologist at Northwestern Medicine. "This is why you should always contact your care team if you see blood of any shade — from bright red to almost black — in your stool."

Causes of Rectal Bleeding

• Hemorrhoids are a common cause of blood in your stool. Hemorrhoids are swollen veins that can develop both inside the rectum and in the skin around your anus. Hemorrhoids are not harmful, but they can cause bleeding when you're passing stool. They can be painful and irritating as well.
• Ulcers, or sores, can develop on the walls of your intestines, causing pain and bleeding. Ulcers are more serious than hemorrhoids, as they can cause substantial internal bleeding.
• Gastrointestinal cancer can cause blood in your stool as well, including colorectal cancer, stomach cancer and esophageal cancer.    
• Inflammatory bowel disease (IBD) is chronic inflammation of your gastrointestinal tract, which can lead to internal bleeding. The two most common inflammatory bowel diseases are Crohn's disease and ulcerative colitis.

Different Shades of Blood in Your Poop

Your stool color can provide clues as to what's happening inside your body:

• Bright red or maroon blood can mean that the bleeding is happening lower in your intestines like in your colon, rectum or anus.
• Black and tarry blood can mean that the bleeding is occurring higher up in your intestines, like in your esophagus, stomach or small intestine.

"It's important to note that these colors can usually tell us where the blood is coming from, but not always," says Dr. Stevoff. "For instance, maroon or red stool could be coming from an ulcer in the stomach, which could be life-threatening because it means blood is coming through really fast in high volume and doesn't have time to turn black. That's why you should always contact your primary care clinician when you see blood in your stool."

Other Reasons for Stool Color Changes

Healthy stool has a medium to dark brown color, but this can vary depending on what you consume. For example, bismuth subsalicylate (used in antidiarrheal medications) and iron supplements can darken your stool. Some foods may also cause a slight variation in your stool color, such as beets, green leafy vegetables and black licorice, as well as food coloring.

See Blood, Seek Care

Often people with chronic hemorrhoids experience blood in their stool regularly, but you should always let your primary care clinician know when you are having any type of bloody stool that is new to you. Your clinician will be able to help identify where the bleeding is coming from and develop a treatment plan for you.