Breastfed Baby Poop Smells Like Rotten Eggs (5 Reasons)

Among new parents, no bodily function is talked about as much as pooping is. From size, to color, to consistency, and even smell, poop can say quite a lot about a baby’s diet and gut health.

Breastfed baby poop smelling like rotten eggs is caused by an increase in the sulfur and sulfuric compounds normally found in poop. This may be due to factors such as the breastfeeding parent’s diet, milk sensitivity, or changes in your baby’s gut microbiome.

A change in the smell of your baby’s poop doesn’t usually signal a problem. It is quite normal and expected even, for baby poop to change as their digestive system develops. This article will help explain a few reasons why your breastfed baby’s poop smells like rotten eggs.

Reasons for Breastfed Baby Poop Smelling Like Rotten Eggs

Parent’s Diet

person holding spoon and ceramic fruit bowl

Small amounts of what you eat and drink can make their way into your breastmilk, causing some minor changes to its composition. Most of the time, this should not affect your baby negatively. 

Occasionally, however, a breastfeeding parent may consume food that their baby is sensitive to or is not yet used to digesting, causing temporary changes to their poop.

Eating foods such as eggs, dairy, red meat, and cruciferous vegetables like broccoli, brussels sprouts, and kale that have a high sulfur content can cause you to produce breastmilk with a higher level of the compound.

Sulfur is an important element that contributes to many body functions. Among other things, it protects and repairs DNA from damage and boosts connective tissue strength and flexibility. Unfortunately,  when your baby consumes breastmilk with a high sulfur content, their poop may come out smelling like rotten eggs.

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Baby’s Diet

Once babies begin eating solids, their digestive systems also begin receiving nutrients in a whole new way. Unlike breastmilk which is easily digested, solid foods have their nutrients hidden in compounds that are harder or sometimes impossible (like fiber) to digest.

This means that once your baby starts solids, their body works harder to digest and break down large compounds from their food into small nutrients that their body can use effectively. 

If you have recently introduced solids into your baby’s diet and notice that their poop now smells like rotten eggs, it may just be their body getting used to digesting a new type of nutrition.

Another reason why your baby’s poop smells like rotten eggs after introducing solids is because it takes more time and effort to digest their food and it is sitting in their system for longer as a result. This is nothing to worry about and will most likely settle the longer your baby eats solids.

Developing Gut Microbiome

gut microbiome

Before birth, babies do not yet have any of the microflora that constitutes the human microbiome. This is why a newborn baby’s first few poops don’t usually have a particularly strong or noticeable smell.

During and immediately after birth, however, parent-to-baby transfer of several strains of beneficial bacteria occurs through breastfeeding and exposure to the parent’s vaginal microflora. These bacteria form colonies on your baby’s skin as well as in their baby’s gut, nose, and mouth.

This bacteria helps your baby digest food, synthesize vitamins and amino acids, and prevent bad bacteria from causing trouble to their immature immune system. The downside is that they often produce odorous compounds as a by-product of their metabolic process. 

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The new rotten egg smell that you are noticing from your baby’s poop may be due to sulfur-reducing bacteria (RSB) that is part of their gut microbiome. While RSB are not harmful, an overgrowth of the bacteria can cause weight loss and malnutrition. 

Milk Sensitivity

Less commonly, breastfed baby poop may smell like rotten eggs due to an allergy or sensitivity to breast milk. Babies who are lactose intolerant often have watery and foul, rotten egg-smelling stools due to a build-up of lactose in their intestines.

Sensitivity to milk protein can cause skin reactions such as a rash around your baby’s lips and mouth and respiratory symptoms such as a runny nose and itchy throat in addition to digestive issues typically seen with other food sensitivities such as diarrhea, vomiting, and an upset stomach.

Most babies eventually outgrow milk sensitivities between 3-5 years old. Until then, it is best to ask your baby’s healthcare provider for guidance on how to manage your baby’s diet and nutrition.

You may be advised to alternate between breastfeeding and using a formula that caters to your baby’s specific sensitivity. In more severe cases, you may be told to transition to a sensitivity or allergen-specific formula to ensure your baby’s continued growth and adequate nutrition.


An infection in your baby’s digestive system can cause their poop to appear different than it usually does. Parasitic, viral, and bacterial infections can make their way to your baby through improperly handled or cooked foods, contaminated water, and contaminated surfaces such as doorknobs, toys, and changing tables.

In addition to foul-smelling poop, infections can cause your baby to have watery diarrhea, and greasy, pale-colored, and sometimes blood-streaked poop. Fever, vomiting, and poor feeding are also common symptoms of gastrointestinal infections.

With proper treatment, most babies recover from gastrointestinal infections completely within 10 days. If you think it is possible that your baby’s poop smells like rotten eggs due to an infection, they will need to be seen by their healthcare provider as soon as possible for medication and treatment.

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What Does Normal Breastfed Baby Poop Look Like?

Generally speaking, poop doesn’t smell great, regardless of whether it comes from a baby or a full-grown adult. A poop that smells bad is not necessarily a cause for concern unless it smells exceptionally or unbearably bad enough to clear a room.  

Breastmilk is easier to digest and moves much faster through the digestive tract than formula does.

In the first 6 weeks of life, breastfed babies should have at least 3 bowel movements a day. Although anywhere from 4-12 poops each day can be normal.

Because babies absorb nearly all components found in breast milk, there is usually very little that needs to be expelled. As your baby’s body gets better at absorbing nutrients from their food, they may start pooping less.

A normal poop schedule for breastfed babies more than 6 weeks old can poop anywhere from once a week to a few times a day. As long as your baby is healthy, gaining weight, and making 6 or more wet diapers each day, the frequency of poops are not usually a cause for concern.

When To Be Concerned?

Babies change rapidly and sometimes seemingly overnight. Their poop changes quite a bit too, as they grow up, develop better digestive systems, and are exposed to new forms of nutrition. Poop that has any of the following characteristics may signal a problem with your baby’s health.

  • Black, sticky, or tarry poop after the meconium has passed may be due to upper digestive tract bleeding
  • Red-tinged or bloody poop can be a sign of lower digestive tract bleeding
  • Poop that has a consistency thinner than toothpaste, is watery, or contains mucus
  • Chalky, pale-colored poop may be due to difficulty absorbing nutrients from breastmilk
  • Hard, dry poop that is difficult to pass or causes your baby abdominal pain