Baby Poop Smell Like Fish? Why and What Should I Do?

The first time you encounter the fishy stench from your little one’s feces, you might be curious about why it happens. So why does baby poop smell like fish? 

In this discussion, I’ll share the top 13 reasons for this smell and help you understand when you should be concerned. Let’s dive right in!

Why Does Baby Poop Smell Like Fish? 

baby poop smell like fish

The fishy odor from your baby poop might be due to teething, introducing solid foods, or an imbalance in gut bacteria.

Infections like rotavirus, salmonellosis, or giardiasis can also cause this smell. Sometimes, formula milk or lactose intolerance might play a role.

Formula Milk

The transition to formula milk can change the smell of a baby’s poop. Formula milk contains mixed ingredients that may not be present in breast milk.

These ingredients can include various proteins, fats, and carbohydrates, each with its own unique odor when broken down during digestion.

Some of these breakdown products can lead to a fishy odor in the stool.

However, please note that while a more pronounced odor is common in formula-fed babies, it doesn’t necessarily indicate a health issue. 

Parents should be attentive to other signs of discomfort or illness, such as abdominal pain, as these could be related to an uncommon condition like irritable bowel syndrome or a urinary tract infection.

Therefore, the choice of formula and the baby’s response to it can contribute to variations in poop odor.

If parents notice consistent or severe changes in their baby’s stool smell, please consult a healthcare professional. They can guide managing potential issues.


Baby teeth coming in the wrong order can be frustrating for parents, and surprisingly, it can also impact the smell of a baby’s poop.

When breastfed babies begin teething, their poop might emit a distinctive fishy smell primarily because of increased saliva production, so infant poop smells like fish.

Teething itself doesn’t directly cause this odor; rather, it’s the interaction of saliva with the baby’s gastrointestinal system that plays a role.

Saliva contains enzymes that aid digestion, and when there’s an abundance of it due to teething, it can affect the composition of the baby’s stool.

The excess saliva can temporarily alter the balance in the baby’s digestive tract, potentially leading to loose stools or even watery diarrhea.

This change in stool consistency can contribute to the perception of foul-smelling feces.

However, please note that these variations in bowel movement are generally considered a normal part of a baby’s development, especially around the age of 6 months when teething typically begins.

Solid Foods (Like Fish Or Eggs)

When your baby diarrhea smells like fish, the solid foods in your little one’s diet might be to blame.

Foods like fish or eggs can cause foul-smelling stools as the digestive tract adjusts to processing new substances.

While this might result in greenish poop, it’s generally harmless. However, watch out for signs of intestinal infections like bloody diarrhea, which could indicate a parasitic infection.

Digestive Process

The fish-like feces of your baby might be linked to the digestive process.

As babies consume food, their bodies break down the nutrients within, and this breakdown can generate various odors, including a fishy smell in some cases.

This odor stems from the specific compounds and byproducts produced during digestion.

Imbalance Gut Bacteria

Imbalance Gut Bacteria

An imbalanced gut bacteria can explain why a baby’s poop smells like fish issues.

Breastfed babies usually have a different gut microbiome than formula-fed babies, which can affect the scent of their poop.

An imbalance can sometimes lead to abdominal pain and other signs of illness, so you should see a doctor to check if your child is suffering from a bacterial or viral infection.

Rotavirus Infection

If a newborn poop smells like fish, Rotavirus infection can be the culprit.

This highly contagious virus primarily affects the gastrointestinal tract. It causes inflammation and alters the digestive process.

The infection can give rise to watery diarrhea and excessive mucus production in the intestines, which can contribute to a foul odor in stool.

The virus’s effects on nutrient absorption and digestion can also result in unusual smells.

Some signs of rotavirus infection, such as severe diarrhea and vomiting, when your child experiences this, prompt medical attention is essential to control the infection and prevent dehydration.

Salmonellosis (Intestinal Infection)

Why does my baby’s poop smell like fish? Salmonellosis, an intestinal infection caused by the Salmonella bacteria, is another reason.

Salmonella bacteria produce toxins and trigger inflammation in the digestive tract.

Consequently, various symptoms will arise, including watery diarrhea and abdominal pain.

The combination of inflammation, toxins, and changes in the gut’s microbial balance can result in a foul odor in stool.


When babies poop smells like fish, there’s a good chance that Giardiasis is the trigger. It is a gastrointestinal infection caused by the Giardia parasite.

Giardia parasites attach to the wall of the small intestine. It disrupts the absorption of nutrients and causes diarrhea.

The parasite’s presence and the body’s immune response can lead to a distinctive, foul-smelling stool that may resemble the smell of rotten fish.

Lactose Intolerance

Lactose intolerance can result in a fishy smell in a baby’s poop due to how lactose is processed in the digestive system.

Babies with this issue lack the enzyme lactase needed to break down lactose.

As a result, undigested lactose enters the colon, where bacteria ferment it. This fermentation process produces gasses and compounds with an unpleasant odor, often described as fishy.

Besides the distinctive aroma, babies with lactose intolerance may experience symptoms such as abdominal pain, gas, and loose stools.

Additionally, I’ve noticed that lactose intolerance can occasionally result in baby poop smelling like vinegar. So, be noted!


Cholera is a serious bacterial disease triggered by the microorganism known as Vibrio cholerae.

It can lead to a fishy smelling baby poop due to the rapid and extensive fluid loss associated with the infection.

Profuse, watery diarrhea is to be expected, which can rapidly lose bodily fluids and electrolytes.

As the body tries to expel the disease, it often produces copious, odoriferous diarrhea characterized by its fishy or rotten smell.

E. Coli

Why does my toddler’s poop smell like fish? Escherichia coli is a type of bacteria that can infect the gastrointestinal tract.

When a baby is infected with E. coli, their poop tends to give off a fish-like smell due to the inflammatory response and changes in digestion.

The infection can disrupt the normal balance of gut bacteria and trigger inflammation in the intestines.

These factors, along with the production of toxins by some E. coli strains, will change the stool consistency and odor.


Malabsorption is when the body has difficulty absorbing nutrients from the food consumed. Due to the incomplete digestion of nutrients, a toddler poop smells like fish.

When essential nutrients aren’t properly absorbed, they can undergo fermentation by gut bacteria. Hence, it produces gasses and compounds with distinctive odors.

Metabolic Disorders

If you notice your toddler diarrhea smells like fish, your little one might be experiencing a metabolic disorder because it affects the body’s ability to process specific substances.

For example, conditions like phenylketonuria (PKU) can accumulate abnormal metabolites in the body, which can be excreted in the stool and produce an unusual odor.

When To Worry Baby Poop Smells Fishy Situation? 

When To Worry Baby Poop Smells Fishy Situation 

When unusual signs like bloody diarrhea, severe vomiting, or persistent abdominal pain accompany it, it’s best to call a doctor.

Also, if the odor is consistently strong and doesn’t go away after a day or two, it’s a source of concerns.

However, occasional variations in poop smell, especially after changes in diet, are generally normal. 

Trust your parental intuition and consult a healthcare professional when unsure or worried about your baby’s health.


That covers everything you need to know should a baby poop smell like fish. In reality, there are several underlying reasons for this problem.

While some prominent signs may immediately reveal the cause, others might require thorough check-ups from a doctor.

Please leave a comment if you still have any queries in mind; I’m all ears.

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