Blue Poop Happens: Here Are a Few Reasons Why
Health ConditionsDigestive Health

Why Is My Poop Blue?

Why Is My Poop Blue?
iStock; Everyday Health
By
Published on November 26, 2025
by
After every bowel movement, you likely check the bowl before flushing — a strategy that's recommended to spot potential digestive issues — but one time you notice a blue tint to your stool, and maybe even a blue film on the water. Is it time to freak out?

The short answer is usually no, according to Pratima Dibba, MD, a gastroenterologist with the Medical Offices of Manhattan in New York City. "Blue stools are mostly related to blue pigment, coloring, or dyes in foods," she says. "Rarely, blue-tinged stools can be due to medications … but mostly, they're related to what you've eaten."

Here's a look at what can lead your stool to change color, how long this might be expected to last, and when you should consult a doctor.

Causes of Blue Poop

Blue is an unusual color for poop — compared with brown, the most common color — and it typically occurs for a couple of reasons.

Foods

Any food made with blue food coloring could be the culprit for blue-tinged stool, says Dr. Dibba. If you eat blue icing on a cake or drink a beverage that's colored blue with food dye, that could be the cause. There are some foods with natural coloring that might result in a bluish tint or flecks of blue in your stool as well:

  • Blueberries, both fresh and dried
  • Purple or black grapes
  • Black plums
  • Black currants
  • Blackberries

Medications

The drug that's best known for lending a blue tint to stools is Prussian blue (Radiogardase), says Dibba. This is a medication used to remove chemical compounds from the body. It’s typically only used to treat people who have suspected radioactive caesium or thallium contamination or non-radioactive thallium poisoning, so it's not a common cause for blue stools.

A compound that’s used more widely and can lead to blue poop is methylene blue (ProvayBlue), also known as methylthioninium chloride. It’s a dye used in some diagnostic procedures, to treat the blood disorder methemoglobinemia, as a component in some drugs used for urinary tract pain, and in rare cases, as a therapy for certain types of shock (including septic and anaphylactic), and malaria. Although it's considered harmless, the dye can lead to stools that are blue or blue-green, and you’d likely also see it released in urine.

Is Blue Poop Dangerous?

Blue poop is most often harmless because it's usually an indication of some type of dye or coloring that's not absorbed into your digestive tract and gets flushed out in your stool instead, says Dibba.

How to Treat Blue Poop

If you're bothered by a blue tint to your poop, the easiest strategy is to simply wait it out, Dibba says. With color changes related to food, it should typically resolve within 24 to 48 hours, she says, though food can sometimes take up to 72 hours to travel through the GI tract.

You can drink more water and eat high-fiber foods as a way to flush out your system faster, she says. But the duration of blue poop will likely be brief even if you do nothing.

When to See a Doctor

Poop that’s blue, or any color that’s not brown, including red — which can sometimes indicate blood in your stool — may be jarring at first. But because it's nearly always related to what you've consumed, it's not likely to prompt a doctor visit, says Ashkan Farhadi, MD, a gastroenterologist at MemorialCare Orange Coast Medical Center in Fountain Valley, California.

 But if the blue tinge (or any other abnormal color) persists after you’ve changed what you eat, and you’re not taking medications known to cause it, he suggests a visit to your doctor.
Changes in your bowel movements that require immediate attention include:

  • Blood in your stool
  • Poop that looks deep red, maroon, black, or tarry
  • Pale, white, or clay-colored stools
  • Persistent diarrhea or constipation that lasts longer than two weeks
  • Nausea and vomiting that occur along with constipation and abdominal pain

"Basically, it's helpful to know what your stool looks like when you're healthy and there are no issues, so you know your baseline," says Dr. Farhadi. "That way, you can detect any issues, such as ongoing diarrhea or very loose stools, or color changes that don't resolve with diet changes."

Particularly if you see blood or blackened stools — which can be an indication of upper digestive tract bleeding — that should be a cue to contact a health professional, he says.

 That doesn't mean it’s automatically an emergency, since it could be related to foods, medications, or supplements such as iron, which can darken stools.

 But it's best to get checked to make sure there isn't a more serious issue, he says.

The Takeaway

  • Blue is not a common color for stools, but it can happen, especially if you eat certain foods that are naturally blue or contain blue dyes.
  • You may experience blue-colored stools if you take certain medications.
  • The blue tinge should resolve within a day or two, but if it persists, consult your doctor, especially if you're experiencing other issues like nausea or pain.

Resources We Trust

EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Is My Poop Healthy/Normal? Canadian Digestive Health Foundation. June 14, 2023.
  2. What Does My Stool (Poop) Color Mean? Cleveland Clinic. February 11, 2025.
  3. Can Food Change the Color of Your Poop? Cleveland Clinic. February 26, 2025.
  4. Zambia Food-Based Dietary Guidelines: Technical Recommendations. Food and Agriculture Organization of the United Nations. 2021.
  5. Prussian Blue (Oral Route). Mayo Clinic. February 1, 2025.
  6. Methylene Blue. Memorial Sloan Kettering Cancer Center. December 12, 2022.
  7. Baumgarten J et al. Fifty Shades of Green and Blue: Autopsy Findings After Administration of Xenobiotics. Forensic Science, Medicine, and Pathology. October 30, 2024.
  8. Bistas E et al. Methylene Blue. StatPearls. June 26, 2023.
  9. Uribel Tabs. National Institutes of Health. January 2024.
  10. Maheshwari N et al. Methylene Blue in Septic Shock: Emerging Evidence, Clinical Applications, and Future Directions. Cureus. June 24, 2025.
  11. How Long Does It Take Food to Digest? Britannica. September 19, 2025.
  12. Changes in Bowel Habits. Cleveland Clinic. September 21, 2023.
  13. Melena (Black Stool). Cleveland Clinic. June 8, 2023.
Meet Our Experts
See Our Editorial PolicyMeet Our Health Expert Network
ira-daniel-breite-bio

Ira Daniel Breite, MD

Medical Reviewer
Castle Connolly Top Doctor

Ira Daniel Breite, MD, is a board-certified internist and gastroenterologist. He is an associate professor at the Icahn School of Medicine at Mount Sinai, where he also sees patients and helps run an ambulatory surgery center.

Dr. Breite divides his time between technical procedures, reading about new topics, and helping patients with some of their most intimate problems. He finds the deepest fulfillment in the long-term relationships he develops and is thrilled when a patient with irritable bowel syndrome or inflammatory bowel disease improves on the regimen he worked with them to create.

Breite went to Albert Einstein College of Medicine for medical school, followed by a residency at NYU and Bellevue Hospital and a gastroenterology fellowship at Memorial Sloan Kettering Cancer Center. Working in city hospitals helped him become resourceful and taught him how to interact with people from different backgrounds.

See full bio
elizabeth-millard-bio

Elizabeth Millard

Author

Elizabeth Millard is a Minnesota-based freelance health writer. Her work has appeared in national outlets and medical institutions including Time, Women‘s Health, Self, Runner‘s World, Prevention, and more. She is an ACE Certified Personal Trainer and a Yoga Alliance Registered Yoga Teacher, and is trained in obesity management.

See full bio
See Our Editorial PolicyMeet Our Health Expert Network