What Causes Blue Poop?

You’re in the bathroom when, suddenly, you look down and see blue poop in the toilet. You immediately think, “I’m dying!”.

Firstly, calm down. While this isn’t necessarily a common symptom, it’s also not a death sentence.

In this article, we’ll explore the possibilities and show you what might be causing your symptom.

Blue Crayons (Children)

blue poopIf it’s a child with blue poop, then it’s possible that they ate a blue crayon. Similarly, your child may have eaten blue playdough.

Fortunately, the manufacturers of these products know that this is bound to happen, and so they make their products nontoxic.

Check the crayon box to see if the blue one is missing. If it is, that could be the culprit!

Bottom Line: In children, seeing blue poop could signify that they’ve eaten something they’re not supposed to (crayons, playdough, etc.).

Blue Curacao or Grape Soda

Blue curacao is a type of liquor that, while delicious, can make your poop turn blue. Ask yourself: did you recently drink this liquor?

If so, that’s most likely the cause for your symptom. Speaking of drinks, you may have also ingested grape soda recently.

Grape soda, like curacao, can cause blue poop. Note, not everyone who ingested grape soda or curacao will experience this symptom.

Bottom Line: Another reason why your stool has changed color is because you’ve ingested grape soda or blue curacao.

Foods That Can Cause Blue Poop

Like beverages, there are various foods that can make your poop turn blue. These include:

  • Blueberries: Blueberries are one of those foods that can influence the color of your stools. Specifically, they can make your stools develop a blue tinge. If eaten in large amounts, they can even make your stools turn black (which is different than a tarry stool).
  • Blue Velvet Cake: Velvet cakes are extremely popular around the world. Originally, they were red. However, eating blue velvet cake is becoming more fashionable. If you have blue poop, it could be that you’ve recently eaten velvet cake.
  • Infant Formula: In infants, this symptom might be caused by infant formula. Mothers have reported changes in their baby’s stool color after switching formulas. This could be due to an increased amount of iron in the formula.

Another food to watch out for is “false blueberries”. These aren’t blueberries at all- they’re a processed food that don’t contain any blueberries.

The manufacturers put blue dyes in these false blueberries, which can explain your symptom.

As a side note, we don’t recommend eating these since they’re loaded with high-fructose corn syrup.

Bottom Line: Your symptom can be due to eating blue velvet cake or blueberries. In infants, it can happen after switching formulas.

Prussian Blue

If someone experiences heavy metal poisoning, then they are usually given Prussian blue.

During a widespread contamination or industrial accident, someone may develop radiation or thallium poisoning.

These capsules can help treat the poisoning. Unfortunately, they can also lead to blue poop.

So, if you’re noticing your stools changing color while you’re taking this capsule, then that’s the reason.

Bottom Lin: Prussian blue is a capsule taken by people with heavy metal poisoning. A side effect is that it can change stool color.


The term porphyria describes a group of diseases that involve the buildup of “porphyrins”. This can affect the nervous system and skin.

As these compounds build up in the body, it can lead to abdominal pain, fever, seizures, chest pain, and more.

These “attacks” can last anywhere from a few days to a few weeks. Another side effect to porphyria is blue poop.

Bottom Line: Your symptom might be due to porphyria, which is a group of diseases characterized by the build of “porphyrins”.

Can it Be Prevented?

The good news is that your symptom can be prevented. The quickest and easiest way is to stop ingesting the foods/beverages causing the change in stool color.

If you’re ingesting a lot of grape soda or blue curacao, then stop drinking it and see if that helps.

Chances are that it will. In children, blue poop is typically caused by the ingestion of crayons or playdough.

These items are non-toxic so there’s nothing to worry about. Finally, in infants, if the symptom persists, change infant formula to see if that makes a difference.

As you can see, most of these causes aren’t life-threatening (they’re just annoying at most).

Bottom Line: You can make your stools return to normal color by not ingesting a lot of blueberries, blue curacao, or grape soda.

When Should You See a Doctor?

If you’ve taken the preventative measures mentioned above, and your blue poop still isn’t going away, then it’s recommended that you see a doctor.

Even though this symptom typically isn’t serious, it’s better to be safe than sorry.

Remember- foods and beverages can play a big role in the color of your stools (even your urine). For that reason, pay attention to what you’re eating.

Ask a Question: If you want to ask a medical doctor a question that hasn't been answered in one of our articles go to: Ask a Medical Doctor About your Symptoms

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