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What could be the cause of sour smelling stool in 10.5 month old infant ?

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Internal Medicine Specialist
Practicing since : 1998
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My 10.5 month old baby boy has had sour smelling diarrhea for a week or so now. The poop is getting more solid but still has this rancid smell. I've been feeding him whole milk "Yo Baby" yogurt every day for its active cultures and avoiding fruits (outside of applesauce and bananas). I'm assuming its a stomach virus. What causes the sour smell and should I be doing anything different? Be concerned? No fever, feels warm to touch but no temp on thermometer, of concern.
Posted Tue, 8 May 2012 in Child Health
Answered by Dr. Jasvinder Singh 41 minutes later
Thanks for posting your query. I can understand your concern for these symptoms in your child.

Since your baby is having rancid smelling free flowing stools for the past few days but there is no accompanying fever and vomiting, so it rules out a virus infection. If the diarrhea is accompanied by fever and maybe vomiting, then it is probably an intestinal viral or bacterial infection. Sometimes in such cases, there is accompanying abdominal pain and loss of appetite. Rotaviral infection is the commonest but it causes very foul smelling, watery, XXXXXXX or brown diarrhea that can persist for weeks.

However to completely rule out any infection, I suggest you to consult a pediatrician and get a stool culture.

From what you have described, it is common for infants to occasionally have one or several stools that are much more loose and foul smelling than usual. This is probably due to a variation in diet or may be idiopathic ( no cause). The foul smell is due to the bacterial action of the intestines on the stools because at this age of life, there is a sudden change in diet from milk to more solid foods. These type of stools can be found for a few days in many normal babies. If there is no fever, abdominal pain, restlessness of the baby and the baby is feeding well, then it is not a cause of concern.

One thing that you can do is instead of whole milk yoghurt give him some soy based formula which gives the intestines some time to heal after the change in consistency of stools. Give him BRAT diet (i.e. bananas, rice, applesauce, toast) or soft easily digestible semisolid diet, white grape juice and oral electrolyte solution.

Hope this answers your query. If you have additional questions or follow up queries then please do not hesitate in writing to us. I will be happy to answer your queries.

Wishing you good health.
Above answer was peer-reviewed by
Follow-up: What could be the cause of sour smelling stool in 10.5 month old infant ? 14 hours later
Thank you for the great advice. The only thing I forgot to mention is that I am still breastfeeding, obviously intermittent with solids throughout his day. I read somewhere that some women's breastmilk when refrigerated and/or frozen, can break down differently (proteins) and create a sour taste. My son has NEVER wanted anything to do with a bottle or sippy cup with breast milk in it.....until a week or so ago when we started adding a bit of fruit juice in with it, to a sippy cup. Could this be a reason for the foul smelling poop? A problem with my breastmilk when refrigerated? Also to note, I removed yogurt from his diet today and am going with the BRAT diet you recommended, however, I just noticed that I myself, have been having very similar stomach issues the last 36 hours or so that I thought I should mention. My stool is very sour smelling as well. Is this common and I'm assuming it could be something we've caught from each other? I am collecting his stool for samples to turn into my pediatrician's office, over the next few days.
Answered by Dr. Jasvinder Singh 13 hours later

Thanks for the follow up and the clarification. If a mother is breast feeding her child, then whatever the mother ingests as food or drug has a direct effect on the child. The foods that you are eating may be responsible for the sour smell of the stools in your as well as your baby's case. It does not look like any contagious gastrointestinal infection. So if you are not having any diarrhea or loose stools, it is unlikely that your baby got transmitted any infection from you.

It does not seem to be related to the addition of grape juice in the stored breast milk but when you store breast milk, follow these measures:

1) Leave about an inch of space at the top of the freezer bag or bottle, to provide space for expansion after freezing.

2) Use sterilized freezer bags and bottles for storing breast milk.

3) Keep the bottles dated so that the oldest breast milk is consumed first.

it is true that the sour taste of the breast milk can develop due to decomposition of an enzyme in the breast milk. So if possible, try giving your infant fresh breast milk and light BRAT diet as suggested.

Hope this answers your query. If you have additional questions or follow up queries then please do not hesitate in writing to us. I will be happy to answer your queries.

Wishing you good health.

Above answer was peer-reviewed by
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