Short answer
Blue or purple stool is almost always caused by blue or purple food dye, or by dark-pigmented foods such as blueberries. It clears within a day or two. If you cannot link it to anything you ate, or stool looks dark purple-red like blood, get it checked.
What causes blue or purple stool?
Blue or purple stool is almost always caused by blue or purple food dye, or by dark-pigmented foods such as blueberries.
- Food dye. Blue and purple dye in frosting, cake, candy, cereal, sports drinks and drink mixes. See food coloring and poop color.
- Blueberries, blackberries and other dark fruits. Their pigments can tint stool deep blue, purple or nearly black.
- Dye in medicines. Some liquid medicines and chewable tablets contain coloring.
Blue stool from food is usually dark blue-green, because the dye mixes with the normal brown of stool.
Can purple stool be blood?
Stool that looks dark purple or maroon can be blood. If there is no blue or purple food or drink that explains it, treat it as possible bleeding. See blood in stool and red stool.
When should you see a doctor about blue or purple stool?
See a doctor if blue or purple stool lasts more than three days with no dye or food to explain it, or if it looks dark purple-red or maroon.
Usually harmless
- You ate or drank something blue or purple, it clears within two days, and you feel well
Call a doctor
- The color lasts more than three days with no dye
- You cannot link it to any food or medicine
Get care now
- Dark purple or maroon stool with dizziness, pain, or a lot of blood
Warning signs to know
These are signs that published medical guidance says need prompt or urgent care. The list is not complete, and ticking boxes cannot tell you whether you are ill. If you are worried, contact a clinician whatever you tick.
Questions people ask
Why is my poop blue?
Usually blue food dye or dark blue foods such as blueberries. It clears within a day or two.
Is purple poop serious?
Not usually. It is most often dye or dark fruit. Dark purple-red or maroon stool with no food explanation could be blood and should be checked.
Can blueberries turn stool blue or black?
Yes. Blueberries can make stool dark blue, purple or nearly black. See a doctor if stool is black and sticky.
Can blue poop happen in babies?
It can after blue-dyed foods or medicines. Call your pediatrician if you are unsure, or if stool is white, red or black.
Sources
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