What to Do About Foul-Smelling Baby Poop?

I believe I’ve told you all before about my eldest’s first poop. I was tethered to the catheter still in the hospital after that c-section. My husband changed her diaper and made a fuss over how gross it was.

It was comical to the point where I buzzed the nurse to have her check my incision. I thought it had ripped open from my laughter.

Breastfed baby poop isn’t quite as smelly as formula-fed baby poop. But poop is poop, nonetheless. And you can’t exactly expect it to smell good.

But sometimes foul-smelling baby poop pops out. And you’re wondering whether it is normal. Why does breastfed baby poop smell like vinegar? Should baby diarrhea smell like vinegar? When should I flip out?

As you know, there will be no flipping out here. But I will tell you when you should contact the doctor about that baby poop. Let’s unwrap the stenchy goodness on the topic of baby poop and the sour smells you may, unfortunately, encounter during the first year.

When does the baby’s poop start to smell?

My husband overdramatized the smell he encountered with that first poop. It’s not that baby poop doesn’t smell in those first few days. But it has a slight odor, the least it will ever have.

The gut will soon become colonized with bacteria, and thus, the smells will increase. This is all totally normal stuff.

For breastfed babies, the poop tends to be less smelly. Formula-fed babies will produce more pungent poops.

Poop smells, as you know. None of us are capable of making one without it stinking.

But for babies, when that poop smell becomes overly foul and even brings tears to the eyes, it may reveal something else is going on.

mother checking out newborn's diaper

I’ll discuss that in greater detail below, but basically, if your baby is growing fine and the color of the poop and the consistency are normal, then everything is likely ok.

Most parents will discover that baby’s poop starts smelling fouler when solids are introduced. That’s at about 6 months of age, so get ready for that! P.U.!

Why does my baby’s poop smell like vinegar?

Foul-smelling baby poop happens sometimes. But when it smells like vinegar, you may, of course, be concerned.

Baby poop is a window into your baby’s health. If it changes in color, texture, and odor and your baby seems upset or isn’t gaining weight, it can tell you something isn’t right.

When breastfed baby poop smells like vinegar or even bottle-fed babies, it could reveal that your baby isn’t digesting her food well.

Another reason may be that she is sick with a cold or some sort of stomach ailment. It can also be present when they are teething.

And yes, some babies may react to food (when solids begin) or milk (when feeding formula).

Let me go a little deeper into these sour-smelling poop possibilities…

It could be lactose intolerance

If your baby’s poop smells sour like vinegar, it could be sensitive to lactose in milk or dairy products. This can happen with formula or with breastfeeding if you consume dairy. Lactose intolerance may cause diarrhea, gas, and bloating, which can be another clue in addition to the stench. If you notice these things, you should make an appointment with the pediatrician.

Baby isn’t absorbing the nutrients well

Your baby should grow and thrive from the milk or formula she gets. But if she’s not absorbing nutrients well, it can lead to foul-smelling baby poop that has an acidic quality. Malabsorption can happen when your baby is sick or with certain disorders. Weight loss and diarrhea are other signs your baby isn’t getting the nutrition she needs from what you’re feeding her, so again, if you see this happening (or smell it!), call the doctor and get the baby checked out.

Baby has food sensitivities or allergies

I mentioned recently in another post how you should note what you eat in a journal. This can be effective for helping you get back your pre-baby body and keep tabs on when your baby seems irritated by the foods you eat.

baby skin allergy treatment at hospital

Some foods are more complex to digest than others and can cause your baby to have sour-smelling poop. Look for mucus or blood in the poop, along with the smell. And if it looks bulkier than usual, too, that’s a clue.

Usually, eggs, dairy, soy, and nuts are the most common culprits. If you notice that baby’s poop smells like vinegar when you are eating these things and nursing or feeding baby solids, and you get a vinegar smell from the poop, it’s definitely worth checking for allergies.

Check for Crohn’s disease

It is not quite as common, but Crohn’s disease could be the reason behind that smelly poop too. It can cause watery and explosive bowel movements that will have a sour smell. Please note that any baby can have this happen randomly from time to time. The key difference is that those with this disease will have this happen ALL the time.

Why does my baby’s poop smell rotten?

When baby poop smells like rotten gas or baby poop smells like sour yogurt, it indicates how long it was hanging out in the intestines. The longer it is there with the bacteria, the more smell it will create.

If it’s a one-off, you shouldn’t worry too much. However, foul-smelling baby poop that happens daily can be a sign of an allergy or intolerance. So, if you change the baby’s diapers and you have a vinegar smell every day, this is definitely something you should bring up with the pediatrician.

What causes acidic poop in breastfed babies?

When your baby consumes large amounts of breastmilk from overflowing breasts, this can lead to lactose overload. You’ll likely see from birth up to 3 months, and it is easy to correct.

Basically, when your breasts flow forth with milk, that large volume is low-fat. It goes through quickly, and thus your baby can’t digest all the lactose you’re pouring into her.

What helps? More fat! And thus, the quick fix here is to ensure you drain one breast before offering the second one. That fattier hindmilk is what she needs. There are specific ways to increase fat content in breastmilk.

If you don’t, you wind up causing problems with lactose. It gets into the lower bowel area, draws extra water, and then ferments the bacteria. This fermentation is what produces that stinky gas and acidic poop.

Then you get gas that causes tummy pain and a baby that seems to want to nurse all the time. She doesn’t; she just wants to feel comforted by the suckling. It will only create a vicious cycle, so please be sure to breastfeed the whole breast first before switching sides.

What should baby poop smell like?

Baby poop will always smell to some degree. I mean, it’s poop! But in the first few days of birth, that meconium will pass, and then you still may not notice much smell from breastfed babies. It can smell a little sweet or even a little like popcorn. Sorry for the gross-out.

But formula-fed babies will always have a smellier poop. It will be pastier and lighter in color too.

Regardless of how you feed your baby, if you notice very smelly poops, changes in color or texture, and a change in how your baby is acting, it could be signaling something is amiss that needs to be checked out.

When should I worry about breastfed baby poop?

Sometimes, when new food is introduced, it can make poop change. And that’s totally normal. But if you notice a sudden change like diarrhea, mucus, blood, or foul smell with the poop, you should have it checked out.

mom changes dirty diaper

First, you should watch for other signs of illness. Obviously, if your baby has a fever, this is likely related to the foul-smelling baby poop.

Any baby with loose or smelly poop here or there is likely fine. It can be a problem if it’s happening daily and several times a day.

Incidentally, diarrhea is a huge problem since it can lead to dehydration. If your baby keeps going through diapers and they’re filled with watery diarrhea, you should ensure she’s getting plenty of fluids to replenish her, or things can get serious.

When it comes to baby poop, you should seek medical attention if any of these things are also happening:

  • Baby is running a fever of 100.4°F or higher in a babies under 2 or 3 months of age
  • Your baby is more irritable than usual
  • Baby is vomiting
  • You notice baby is in abdominal pain
  • There is abdominal distension
  • Your baby makes 10 or more watery stools within 24 hours
  • The stool is bloody
  • Baby is dehydrated (hasn’t peed in over 8 hours, or the pee comes out very dark)

In general, if your baby’s poop smells like vinegar, fish, ammonia, popcorn, or anything else unusual, don’t panic. Many times, it’s just a one-off or something in the diet causing it.

But if things persist, make an appointment with your pediatrician. And obviously, if any of those signs I just listed above are coming in with that foul-smelling baby poop, seek medical attention immediately.

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