Reference guide
A complete reference for every common cause of unexpected color changes in stool or urine — organized by what you see, with the mechanism, timing, and when it clears. If you already know what you ate, use the lookup tool for a direct answer.
All entries sorted by clearance time. Click any name to open the full lookup result.
| Name | Color | Onset | Clears |
|---|---|---|---|
| Activated charcoal med | Black | Next BM | 1–3 BMs |
| Acai food | Blue-purple | 6–12h | 24–36h |
| Broad-spectrum antibiotics med | Green | Days | While taking |
| Beets food | Red / pink | 4–12h | 24–36h |
| Blackberries / elderberries food | Blue-black | 6–12h | 24–36h |
| Black licorice food | Dark | 12–18h | 24–48h |
| Blueberries food | Blue / green | 6–18h | 24–48h |
| Carrots / sweet potato food | Orange (skin) | Weeks | Weeks |
| Dragon fruit (red) food | Red / pink | 6–12h | 24–48h |
| Green food dye food | Green | 6–12h | 12–24h |
| Iron supplements med | Black / dark | 12–24h | While taking |
| Matcha / spirulina / chlorella food | Green | 6–12h | 12–24h |
| Metformin med | Green / loose | Days | 2–4 weeks |
| Pepto-Bismol med | Black | 6–18h | While taking |
| Phenazopyridine (AZO) med | Orange (urine) | 1–2h | While taking |
| Red / purple cabbage food | Blue / green | 6–12h | 24–36h |
| Red food dye (Red 40) food | Red / pink | 6–12h | 12–24h |
| Rifampin med | Orange-red (all fluids) | Hours | While taking |
| Senna med | Yellow-green | 6–12h | 12–24h |
| Spinach / kale food | Green | 6–16h | 24–36h |
| Squid ink food | Black | 8–16h | 12–24h |
| Tomato juice / paste food | Red-orange | 8–18h | 24–36h |
| Ube (purple yam) food | Purple / blue | 6–12h | 24–36h |
What foods cause red or pink stool?
Beets are the most common culprit — the pigment betacyanin isn't fully broken down by about 1 in 7 people and passes through intact. Red-fleshed dragon fruit has the same pigment. Red food dye (Red 40) at high doses and large amounts of tomato paste can also cause reddish stool. These are all completely benign and clear within 24–48 hours.
What causes black stool other than blood?
Iron supplements are the most common benign cause — unabsorbed iron forms black iron sulfide in the gut and is expected on every iron supplement label. Activated charcoal causes dramatically black stool and clears in 1–3 bowel movements. Pepto-Bismol (bismuth subsalicylate) reacts with gut sulfur to form bismuth sulfide, also black. Large amounts of black licorice and squid ink pasta can darken stool as well. If you haven't consumed any of these, black or tarry stool warrants a call to your doctor.
Why is my stool green?
Green stool most often comes from large amounts of green foods — spinach, kale, matcha, spirulina, chlorella, or green food dye. It can also result from faster-than-normal gut transit, where bile doesn't fully break down before leaving the body (bile starts out green-yellow and turns brown as it's metabolized). Senna laxatives and metformin both cause this by speeding transit. Some antibiotics alter the gut bacteria that process bile, with the same effect.
What foods cause blue or purple stool?
Blueberries, blackberries, elderberries, acai, ube (purple yam), and red/purple cabbage all contain anthocyanins — pigments that partially survive digestion and can visibly color stool blue, purple, or blue-green. The effect is more pronounced with large servings. Red/purple cabbage is particularly interesting because its anthocyanins are pH-sensitive: they can appear blue, green, or purple depending on gut acidity.
Does beet-red stool mean something is wrong?
Not if you ate beets in the last 48 hours. The pigment betacyanin isn't broken down by about 1 in 7 people — it passes through intact and colors stool and urine pink or red. This is a quirk of individual gut chemistry, not a sign of illness. It clears within 24–36 hours of your last beet. The only reason to be concerned is if the red color appears without any dietary explanation — then it's worth calling your doctor.
What medications turn urine orange?
Rifampin (rifampicin), an antibiotic commonly used for tuberculosis, famously turns all body fluids orange — urine, sweat, tears, and saliva. Patients are warned about this in advance because it can permanently stain soft contact lenses. Phenazopyridine (sold as AZO) is a urinary pain reliever that turns urine a very bright orange and is used as a dye test to confirm urinary tract infections.
Color changes that have a clear dietary or medication explanation are virtually always benign. See a doctor if the color change has no obvious cause, if you're also experiencing abdominal pain, fever, or significant changes in how you feel, if black stool is sticky or tarry (different from the uniform black of charcoal or iron), or if red coloring appears in urine without a dietary explanation. When in doubt, a quick call to your doctor costs nothing and rules out the small number of cases where color change is a signal worth investigating.