The normal colour of poo ranges from medium to dark brown. That brown colour comes from bilirubin, a yellow-orange waste product made when your body breaks down old red blood cells. Bacteria in your gut finish the job, turning bilirubin into a substance called stercobilin — and stercobilin is what makes stool brown.
Shades of brown are normal. So are occasional greens, and even brief changes after certain foods. What matters more than any single colour is whether a change sticks around and whether it comes with other symptoms.
What Is The Normal Colour Of Poo?
Brown is the expected colour, and the range runs from light brown to dark brown depending on diet, hydration, and how long stool spends in the colon. The longer it stays, the darker it tends to get, because bile pigments continue to break down.
Colour alone is a weak signal. Doctors rarely diagnose anything from stool colour by itself. What they look at is the whole picture: how long a change has lasted, whether it is consistent, and whether there are other signs like pain, weight loss, fever, or bleeding.
One thing worth knowing: stool colour is not a reliable measure of digestive health on its own. A person can have perfectly brown stool and still have a medical problem, and a person can have an odd-coloured stool one day and be completely fine. The colour is one clue among many.
What Does Each Stool Colour Mean?
Most colour changes trace back to food, supplements, or how fast stool moves through the gut. A few colours are worth paying closer attention to. Here is a practical breakdown.
| Colour | Common causes | When to pay attention |
|---|---|---|
| Brown | Normal bile breakdown; typical diet | No action needed |
| Green | Leafy greens, food dye, iron supplements, fast transit time | If persistent with diarrhea or cramping |
| Yellow, greasy, foul-smelling | Too much fat in stool; fast transit; trouble absorbing fat | If it floats, sticks to the bowl, and persists |
| Black, tarry | Iron supplements, bismuth (Pepto-Bismol), or bleeding higher in the gut | If it looks like tar and you are not on iron or bismuth — seek care |
| Red, blood-streaked | Beets, food dye, or bleeding lower in the gut such as hemorrhoids | If blood is unexplained or ongoing — seek care |
| Pale, clay, or putty-coloured | Not enough bile reaching the stool | If persistent — see a doctor promptly |
This table covers the main categories. Each one deserves a closer look, because the details matter more than the colour name.
Why Does Poo Turn Green?
Green stool is usually harmless and often has an obvious cause. Bile itself is green. When stool moves through the colon quickly, there is less time for bacteria to convert the green bile pigments into brown stercobilin, so the green shows through.
Common triggers include eating a lot of spinach, kale, or other leafy greens; food dyes used in drinks and candy; and iron supplements, which can turn stool dark green or black. A short bout of diarrhea can also produce green stool simply because of fast transit time.
Green stool that comes with ongoing diarrhea, cramping, or urgency is worth mentioning to a doctor. It may point to an infection or a condition that speeds up digestion, but colour alone does not confirm either.
What Causes Pale Or Clay-Coloured Stool?
Pale, clay, or putty-coloured stool is the colour change that most deserves medical attention. It usually means bile is not reaching the intestine in normal amounts. Bile is what gives stool its colour, so when the flow is blocked or reduced, stool loses its brown pigment.
Possible causes include a blockage in the bile ducts, liver conditions, and problems with the gallbladder or pancreas. Some medications and imaging contrast dyes can also lighten stool temporarily.
Pale stool is more concerning when it comes with yellowing of the skin or eyes (jaundice), dark urine, itching, or pain in the upper right abdomen. Those signs together suggest bile flow is disrupted, and they warrant prompt medical evaluation. This is not a wait-and-see situation.
When Does Black Or Red Stool Signal A Problem?
Black and red are the two colours people most often worry about, and the concern is reasonable. Both can be caused by bleeding in the digestive tract, though both also have harmless explanations.
Black, tarry stool can come from iron supplements or bismuth-containing medicines like Pepto-Bismol. It can also come from bleeding higher up in the stomach or small intestine, because blood turns black as it is digested. The key difference is texture: bleeding produces a sticky, tar-like stool with a distinct foul smell, not just a dark colour. If you are not taking iron or bismuth and your stool looks like tar, get medical help.
Red stool can come from beets, food dyes, or red gelatin. It can also come from bleeding lower in the colon or rectum, such as from hemorrhoids or other sources. Bright red blood that streaks the stool, coats the toilet paper, or drips into the bowl should be checked by a doctor, especially if it happens more than once.
Any black or red stool along with dizziness, weakness, or a racing heart is a reason to seek emergency care. Those symptoms can point to significant blood loss.
What Foods And Medicines Change Stool Colour?
A surprising number of everyday things can shift stool colour for a day or two. Knowing the common culprits can save you a scare.
- Iron supplements — dark green or black stool
- Bismuth medicines (such as Pepto-Bismol) — black stool
- Beets — red or pink stool
- Leafy greens and green food dye — green stool
- Blue or purple food dye — can sometimes produce green stool
- Licorice — dark stool
- Some antibiotics and other medicines — variable changes
If a colour change lines up with something you ate or started taking, and it clears up within a day or two, it is usually not a concern. If the change persists after you stop the suspected cause, or if you cannot identify a cause, that is when to ask a doctor.
When Should You See A Doctor About Stool Colour?
Most colour changes are harmless and temporary. A few patterns are worth a medical visit. See a doctor if pale or clay-coloured stool persists, if black tarry stool appears without an iron or bismuth explanation, or if red blood shows up in your stool more than once.
Also seek care if a colour change comes with other symptoms: ongoing diarrhea, cramping, unexplained weight loss, fever, jaundice, or feeling unusually tired or weak. Those combinations carry more weight than colour alone.
For adults over 45, or anyone with a family history of colorectal problems, new and unexplained changes in bowel habits are worth mentioning at a routine visit. Stool colour is not a screening test for cancer, and it should not be treated as one — but it is one piece of information your doctor can use alongside other findings.
Frequently Asked Questions
Is it normal for poo to be different colours?
Yes, occasional colour changes are normal and usually trace back to food, supplements, or how fast stool moves through the gut. A colour that persists for more than a few days, or that comes with other symptoms, is worth checking with a doctor.
What does green poo mean?
Green stool usually means bile moved through the colon quickly, or that you ate something green or took iron. It is rarely a sign of a problem on its own, but ongoing green stool with diarrhea or cramping should be evaluated.
Can pale poo be serious?
Pale or clay-coloured stool can signal that bile is not reaching the intestine, which may point to a liver, gallbladder, or bile duct problem. Persistent pale stool, especially with jaundice or dark urine, needs prompt medical attention.
Does black poo always mean bleeding?
No. Iron supplements and bismuth medicines commonly cause black stool. Black stool that looks like tar, smells strongly, and appears without those causes should be checked by a doctor.
