What goes in must come out — and it usually comes out in shades of brown. So it can be quite a surprise if your poo is suddenly red, green or orange.
In some cases, crayon-colored doo is a clue that there’s a medical problem, says gastroenterologist Christine Dr. Lee, MD. But more often than not, it comes down to diet.
“A lot of foods we eat can change the color of a bowel movement,” Dr. Lee says.
The science of stool color
Stool gets its brown hue from bile, a greenish-brown fluid that aids digestion. “But the exact shade varies from person to person and from day to day,” Dr. Lee says.
Different people produce different amounts of bile, due to causes such as genetics and the health of the gallbladder (the body’s bile storage unit). And even within your gut, bile levels naturally fluctuate over time.
“Variability is the norm,” says Dr. Lee. Factor in the influence of the foods you eat, and you’re looking at a rainbow of possibilities.
Here are common causes of colorful number twos.
Green vegetables
Shades of yellow and green are common hues on the poo color wheel. But if you eat a lot of dark, leafy greens, you might be surprised with bright green poop.
Beets
“Beets tend to scare people,” Dr. Lee says. That’s because a big serving can turn your stool a (harmless) blood-red color.
Blueberries and cherries
Cherries can turn the stool reddish, while blueberries can paint your poo shades of deep blue or even black. Dr. Lee says in both cases, you’d have to eat more than a handful to see such rainbow shades. (One more reason to avoid an all-blueberry diet.)
Carrots
All that beta carotene is good for you, but it can turn your waste orange. “You’d have to eat a lot of carrots, though,” Dr. Lee says. “We tend to see this more in people who guzzle carrot juice.”
Food dyes
Artificial food coloring can go in one end and out the other, turning stool to just about any shade in the rainbow. And if you scarf handfuls of rainbow-colored candy, the colors might mix to turn your poo black. Food dyes tend to change stool color more often in kids, who are (possibly) more likely than their parents to eat an entire bag of colorful candy in one sitting.
Supplements and medicines
Medicines can do weird things to the color of your bowel movements. Some antibiotics reportedly tint them yellow or green. And that bubblegum-pink Pepto-Bismol® you swallow for an upset stomach can turn them jet black.
When should you worry about the color of your poop?
If you eat a ton of blueberries or go overboard on the carrot juice, expect it to affect your stool color for a couple of days. But if the color changes persist, or you can’t connect them to anything you ate, it might be a sign for concern.
Some of the more worrisome colors:
- Red to black: Red or black poop can be a sign of bleeding in the gastrointestinal tract. “Blood in the stool can be anything from bright red to maroon to black, depending on where the bleeding is happening in the GI tract,” Dr. Lee says.
- Gray: Pale or clay-colored stool can indicate a problem with the pancreas or bile ducts.
In both cases, Dr. Lee recommends calling your doctor. Also check in with your doctor if you have other symptoms, such as diarrhea, fever or pain. “Ask yourself: How are you feeling? Put it into context,” Dr. Lee says. “If you feel normal and don’t have diarrhea, 99% of the time, colored stool stems from something you ate.”
