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smelly bowel movements in babiesPin

Mom’s Question:

What are the reasons for really smelly bowel movements in babies? My baby’s poop smells really bad!

My daughter is 7.5 months old, she is on Similac formula, Nestle rice cereal, and Heinz baby food, and her stool is green, mucousy like and it smells really strong. I have never known a baby (which I have been around a lot of) to have this strong smell to their stool.

I was just wondering if this is something to cause concern or if it is a side effect of either her food formula or teething.

Vanessa (B.C. Canada)

Easy Baby Life:

Reasons For Smelly Bowel Movements in Babies

The smell of babies’ stools can vary a lot just like with adults. Here are some possible reasons to consider when your baby’s poop smells really bad:

1. What they eat – What babies eat as well as their health will make the smell more or less strong. Breastfed babies often do not have strong smelling stools. A study from 2001 found that the stools of formula-fed babies contained a lot more odor-causing sulfur gases than breast milk poop. When a baby starts eating solid foods, the feces will change again; often to the worse when it comes to smell.

2. Lactose intolerance or some allergy can also lead to foul-smelling stools. So to test this, try to eliminate all cow’s milk from your baby’s diet and see if it helps.

3. Infections – In addition to these normal diet-related variations, the baby’s stools can also be affected by a stomach bug, a cold, or some food intolerance.

4. Rotavirus – A strong smell and very frequent pooping can indicate Rotavirus, regardless of poop color. Rota virus has other symptoms too, like fever, nausea and belly cramps, and young babies often become very sick from this virus. Since you don’t say that your baby is ill, this virus is most likely not the reason for her smelly poop.

5. Lactose overload – Green poop, a strong smell, and gas can be due to lactose overload, something that can happen if breastfeeding mom has an oversupply. Now, since you are not breastfeeding, this is not relevant for you right now. Did you breastfeed before? Oversupply can actually also lead to traces of blood in the poop.

6. Teething – An unexpected reason (at least it was for me) – is that the baby is teething. Despite a complete lack of research studies on this, many parents agree that their babies’ stools suddenly smelled like vinegar just before one of their baby’s teeth popped.

A sudden shift in the smell, and especially if combined with a change in consistency to the worse (diarrhea, gas, or mucus for example) often indicates that something is wrong.

In addition to watching your baby for other signs of illness or teething, you can also then think back on any new foods recently introduced, and take them away to see if it helps.

Since there are so many reasons for smelly bowel movements in babies, the best you can do as a parent is to look for other signs of teething as well as illness and also think back on any introduction of new foods or formula. If your baby seems to be ill, consult a doctor of course.

P.S. Here are two excellent reference books for baby health issues and injuries:

More Baby Poop Issues

What’s your experience of smelly bowel movements in babies? Join the discussion! :-) Add your comments below or return to Baby Poop Q&A.

This Post Has 9 Comments

  1. Ana

    My 9-month-old son has really smelly poop and I’m wondering if I should be worried. His poop is the normal everyday color from the baby food I give him, yes he is teething and yes he is on Similac sensitive formula. So what should I do

  2. Annie

    I have been going through the exact same thing with my 9-month-old son, for almost 2 weeks. The only new foods I’ve given him are Yogurt Melts and Cheerios. He has eaten my yogurt and baby cereal before with no problem, so I thought it shouldn’t be the new foods. He IS teething and they are hurting him… I hope it is the teething. How interesting.

    1. Maria

      You are giving a 9-month baby Cheerios. Why? They contain a lot of sugar.

      If the stool is green, take the baby to the doctor. Rotavirus is associated with green stool and a strong smell.

      1. Annie

        What’s the big deal with cheerios?? I have been giving them to my little girl since she was 6 months and her pediatrician suggested it!

        Thanks for the tip on rotavirus, though, I’ll have to check that up!

  3. Minna

    It could also be an allergic reaction. We had a similar problem with my 10-month old after I gave her wheat cereal! Try eliminating it for a few days and bring it back to experiment. They smell more with solids too!

  4. teething

    More than likely it the teething. My daughter experienced the same type of smelly diapers. It almost smells acidic. It will eventually go away just bare with it when those pearly whites pop threw it will be worth it believe it or not.

    1. Vanessa

      Yes that’s what it smells like acidic kinda i cant wait for the those teeth to come in and the smell. Thank You

  5. Angel Munro

    My 2 1/2 year old has green poop with a jelly slimy green jelly ooze that’s mixed in as well as all over its been this way last 3 days. And yesterday she pooped 4 times. I’m woundering what this is. I’m planning on taking her to doctor tm. I saved the pull up and wrapped it up so they can test it. But I’ve never ever seen this. Please if you have seen or experienced this let me know

    1. Paula Dennholt

      Hi Angel,
      Did you sort this out? Green poop can sometimes be related to viruses, like a cold. It is usually not dangerous, but of course should be sorted out.

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