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What Are the Black Strings in Baby's Poop? (4 Possible Causes)

What Are the Black Strings in Baby’s Poop? (4 Possible Causes)

Medically reviewed by

Dr. Nicole Nabatkhorian
Dr. Nicole Nabatkhorian

MD / PGY-2 Pediatrics

Disclosure: Some of our articles contain links to recommended products or services in which we may receive a commission if you make a purchase.

As a parent, seeing something weird in your child’s poopy diaper can be disconcerting! There are many questions that might pop up. Is this bad? Is my child sick? Did I feed them something dangerous? Do we need to go to the doctor? You may find yourself wondering what are the black strings in baby’s poop?

Black strings or worm-like pieces in baby poop are most likely undigested bananas. Your baby’s digestive tract is still maturing and certain foods (or parts of food) may be more difficult to process. Babies also poop frequently so it’s not uncommon for food not to be fully processed.

So let’s get a little deeper into this and identify what the black strings in baby’s poop might be.

What are the black strings in baby’s poop?

If you find black strings or worm-like substances in your baby’s poop, there are several common sources that are not causes for concern.

The most common reasons for black strings in baby poop are:

  • Undigested banana or fruit
  • Hair, a thread, or other swallowed objects
  • Stringy mucus
  • Meconium

If you’ve ever wondered why does my baby have black strings in their poop, let’s take a look at each one of these items to determine how it happens.

Undigested banana or fruit

A common cause of stringy black in a baby’s poop is the fiber from bananas and other fruits. You’re likely going to notice black strings in 6-month-old baby poop since this is right around the time they’re starting to eat solid food.

One of the reasons we feed bananas to our children is the fiber they contain; however, if they consume too much, they cannot process it fully. Bananas are soft and easy for babies to consume, and most children love the taste as well, which can lead to them eating more than their tiny little bodies can process in a single day.

Eating a lot of bananas isn’t necessarily harmful, but it would be best to lessen the amount so their system doesn’t have to work so hard.

Fiber strings in baby poop isn’t a cause for concern, but it is a good indicator to cut back (not cut out) their daily banana intake.

Once your baby old enough for finger foods, bananas make a great option!

Stinky diaper

Hair or thread

If the child is crawling or toddling, there is also a possibility of the black strings being hair or thread of some kind. Remember, children put just about anything they can get their hands on in their mouths!

So, if they find a piece of string from a blanket or some hair that fell off the hairbrush, they will likely put it in their mouth. Since your baby’s body doesn’t digest things like hair or threads, they just pass through and come out the other end.

The best way to tell the difference between fruit fiber and string or hair is that fruit fiber does not hold together while you are wiping the baby’s bottom. Instead, it comes apart in little clumps or small, dirt-like pieces. Hair or string, on the other hand, stays in one piece while you are trying to wipe it away.

If it is string or hair, pull VERY gently, and if it can’t be easily removed, LEAVE IT! This means it hasn’t fully been pushed through the digestive tract and you want to avoid causing any pressure in there.

If it still has not passed through in a couple of days, contact your pediatrician for advice on how to assist the string or hair to pass through fully.

Depending on the situation, the doctor might recommend:

  • Ensuring that your baby is drinking adequate water
  • Adding more fibrous foods to baby’s diet
  • Bringing the baby in for an examination

In my experience, I have never seen it take more than a day to pass in any of my children. Although rare, medical intervention might be required to remove the hair or thread from your baby’s digestive system.


Black strings can be caused by mucus in the poo and is not a concern if your baby is still very young. If your child is a little older (2-4+) then pay close attention to the texture, size, and the child’s behavior.

While the digestive functions are still developing, there can be some mucus that needs to be passed through that’s leftover from while the child was still in the womb.

You can easily identify if it is actually mucus as it has the same texture and looks like when you have a badly running nose or cold. Unlike nasal mucus, this is black or dark brown in color due to it being mixed with the toxins that are expelled during normal bowel function.


Meconium is a substance that lines the baby’s stomach during pregnancy and is usually released after birth over the first few days to weeks. It’s also known as baby’s first poop and helps protect sensitive intestines while they are forming.

Meconium is typically dark brown, green, and has a tar-like texture. If you see black strings in baby’s poop within the first few days after birth, it could be traces of meconium left over.

Seeing it present in little one’s stool only means that their tiny body is adjusting well to the outside world and isn’t a cause for concern.

Is black string in baby’s poop normal?

There are many variations of normal when it comes to the color and texture of baby poop. If you’ve ever wondered what are the black strings in baby’s poop, you’ll be glad to know black stringy poop for infants is not uncommon at all.

Almost all children will have this at some point in their early months, but it is most likely to happen in the first few weeks after the baby comes home from the hospital.

The primary cause of this is undigested food, milk, or even mucus in the baby’s stomach. The little one has only started feeding through their digestive tract after birth so their stomach lining and intestines are still getting used to processing nutrients that are not fed directly to them via the umbilical cord.

The black stringy poop normally goes away on its own after a few short weeks.

Dirty diaper

When should I worry about black stringy poop?

There are a couple times when black stringy poop would be a concern. Whether you’re noticing black strings in breastfed baby poop or formula-fed baby poop, it’s important to know what may be a cause for concern.

Of course, in all cases, always rely on the opinion of a medical professional first and do not hesitate to call if you think there is reason for concern.

With that said, there are two big factors to consider if you are dealing with black stringy poop:

  • Other symptoms
  • Excessive quantities of string or hair

Let’s take a look at both of these issues.

If it’s accompanied by other symptoms

A food allergy or intolerance may cause some unpleasantness in the diaper, but it is usually combined with a runny nose, mild fever, and sometimes small traces of blood in the stool as well.

Your baby’s backside will likely be inflamed a bit, and a strong diaper rash may also occur.

The most common sources of food intolerance or allergies are:

  • Peanuts
  • Eggs
  • Soy
  • Milk
  • Wheat (gluten)
  • Tree nuts like cashews
  • Fish and shellfish

If you think your baby might be dealing with an allergy or food intolerance, it is best to make an appointment with her pediatrician right away to have it evaluated.

If your baby is displaying severe allergic symptoms, such as trouble breathing or lethargy, take your baby to the hospital immediately.

Diaper rash from food allergy or intolerance

If it’s more than a little bit of ‘string’

While the occasional hair or string in your baby’s poop is grosser than concerning, a lot of it is a different matter.

Since not even adult digestive systems can process hair, a large clump may not be able to pass through by itself. If this is the situation, give it some time (about a day) and pay close attention to the child’s bowel movements. If the bowel movements slow, or appear painful, or even stop entirely, seek the help of a medical professional.


What causes my baby to have mucus in their stool?

A small amount of mucus in your baby’s stool typically isn’t anything serious. This can happen sometimes during teething. However, if your baby consistently has large amounts of mucus in their poop, it may be due to an underlying issue or illness and should be checked by a doctor.

What causes a baby to have green poop?

Baby poop can be a lot of different colors depending on how old they are and what they’re eating. Meconium, or a newborn baby’s first poop, can sometimes look green. Green poop can also be normal when you first start feeding your baby solid food.

What are the black strings in breastfed baby poop?

Black strings can occur in baby poop whether they’re breastfed or formula fed. If your baby is eating solid food, the black strings are likely undigested food or fruit fibers, typically from a banana. It can also be due to your baby swallowing a hair or thread.


If you’ve ever wondered what are the black strings in baby’s poop, you understand it can seem concerning at first. In most cases, it’s not a problem and is simply caused by baby eating too much fruit or swallowing something that will make its way through their digestive system.

Joshua Bartlett
Joshua Bartlett

My name is Joshua Bartlett I run this blog with my wife Jarah. We have more than 11 years of parenting experience including three girls and one boy. I started this blog in late 2018 when I realized that I was dealing with baby-related issues on a constant basis…please read more about me here!

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