Baby Poop Smell Like Fish

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Baby Poop Smell Like Fish

It often happens that baby poop smell like fish. This is usually common with babies that are fed with formula instead of mothers’ breast milk. Compared to breastfed milk, infants that are fed on formula need a longer time to digest the milk, thus this formula milk stays in the baby’s intestines for a longer time.

This means that it takes time for the bacteria to multiply in the baby’s digestive system. Those bacteria that are created in the intestines are the reason why baby poop has a stinky smell, and very often why baby poop smell like fish. Which is not so common for newborns that are breastfed. 

This is when the intestines do not have sufficient absorption of nutrients, they tend to stay in the intestines for a long time, and bacteria and fishy smell appear. Babies who are breastfed have a yellow sparse and not so fragrant poop. While babies are fed artificial milk, their stool appears to be dark yellow to brown, denser coexistence, and more fragrant. 

If this odor persists for a long time then it may be time to visit your pediatrician. There may be something wrong with your baby’s digestive tract, or your baby’s digestion is bad in general. It is usually not dangerous and is solved with a probiotic or other supplement prescribed by your baby’s health care provider. 

For those infants that are being fed with formula, it often happens that parents change the type of milk they are giving to their newborns. You need to find the right milk that will help your baby digest food easier and more effectively. 

The cause of a baby poop smell like fish may even indicate some serious problems. For instance, it can be the cause of bacterial or viral infection of the baby’s stomach which is a much more serious matter and requires medical care.

Indications for infection are diarrhea, fever, moody behavior, and frequent crying. In those situations, the stool is usually watery and stinks of rotten fish or the baby has gases that smell like rotten eggs.

When should I worry about baby poop smell?

In the first few days of the infant’s life, its stools have almost no odor. However as time passes by, and the bacteria colonize their gut, their stool becomes more smelly.  This is a normal process because food is retained in the intestines where the bacteria is formed and the poop becomes fragrant. 

However, if your baby’s stool becomes smellier, especially foul-smelling, it might be a sign of allergies that your baby is having to certain foods or products. If a strong smell lasts longer than a few days, make an appointment with your child’s pediatrician to find out if an allergy test is required.

You should also take your newborn to visit a doctor if the baby has diarrhea along with a fever. On the other hand, if the baby has more of a hard and dry stool,  it is likely that the baby is constipated.

In any case, the visit and short examination won’t do any harm to your child. So, we advise you to always be cautious and listen to what your health care provider recommends. 

Some signs that can help parents realize that something is not good with the baby’s stool are its smell, color, and shape. If baby poop smells different than usual, e.g. odor of alcohol that persists for a longer time, parents should consult a professional.

If your little one has green and smelly poop, it’s probably because the baby is not getting enough fat from the milk. This happens when the baby eats faster than usual, and in those situations when the newborn is greedy when being breastfed or bottle-fed.

Another reason could be the mother’s diet. Sometimes babies can be sensitive to certain products that the mother is eating and then transfer that to the baby through the milk. Newborns are usually reactive to dairy products, or even spicy food. Therefore it’s important for breastfeeding mothers to take care of what she’s eating, as well as to try to have a mild diet as much as possible.  

When babies are small they often change the look and consistency of their stool which is quite normal. But, if your baby has smelly whitish poop, it may indicate indigestion or liver problems, even when baby poop smell like fish for a longer time. The baby’s stomach may be inflamed, contaminated, or infected with a virus if there is red or pale red, smelly, or mucus-filled poop. 

Your baby needs to be taken to the doctor right away for appropriate medical attention. All these things are indicators that there is something wrong with the baby’s digestive tract. So, when you feel a bad smell of the baby’s stool, along with other symptoms, make sure you seek a doctor’s opinion so your baby can get the proper care.

What does infected baby poop look like?

Baby Poop Smell Like Fish

Newborns that have infections will probably have a green stool. In the extreme cases where irritation is present, blood can also appear in the baby’s poop. However, when a bacterial infection occurs, it is not uncommon to see mucus in the baby’s stool accompanied by blood.

An infection caused by either the virus or bacteria, known as stomach flu, can irritate the baby’s intestines and may trigger inflammation. Poop in a baby with this condition is mucus-filled, while other symptoms are fever and irritability that are almost always an indicator of stomach flu or infection.

What does teething poop look like?

Baby Poop Smell Like Fish

Stools may become a bit loose during teething due to the increased saliva production. However, this type of poop consistency can also be a sign of a much more serious infection. In order to avoid any possible complications, contact your newborn’s healthcare provider. Do this especially if the baby’s stool becomes watery, as your baby may become dehydrated.

When the time of teething comes, many parents claim that the baby’s stool has changed. They have mostly stated that the changes were regarding the color of the poop, turning to a more green or darker color than it used to be. Besides that, the poo was also a bit different consistency. It becomes runnier, watery, and even frothy-looking as teething progress.


After the birth of a child, the time of the first diaper change can be somewhat stressful for parents. As time passes by, parents get used to it, and they don’t even notice the smell of the baby poo. This is because, in the earliest stages of an infants’ life, the baby’s stool has no specific odor. 

A bit later, parents can notice the changes in the smell as well as in the texture of the baby’s stool. Sometimes baby poop smell like fish and in those cases, parents tend to be very worried. One should not be worried since the smell is the result of the baby’s digestive tract needing a longer time to digest the milk. 

This especially refers to the babies that are fed on the milk formula. This type of milk stays in the intestines a bit longer so the bacteria have more time to multiply in the baby’s digestive system. Due to the bacteria that are produced in the baby’s intestines, your infant’s poop smells stinky.

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My name is Catherine. I'm a Mom and one of the avid writers working on HerScoop!