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  • Post last modified:November 7, 2021
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Introducing cow’s milk to a baby or toddler can lead to some changes in their poop color and consistency.

This 1-year-old baby got yellow stools with a bad smell after introducing cow’s milk. Can you relate?

1-year-old-yellow poop cow's milk

Mom’s Question:

We introduced cow’ milk to our one-year-old daughter two weeks ago. She has approx 150ml cow’s milk plus 400ml toddler milk each day. She eats a balanced diet and I have had no problems in the past.

Since this change she has had loose (not diarrhea) stools which are yellow (similar to when they are very young) which have a strong bad smell. She also seems very irritable. Any advice, please?

Smelly, Runny, Yellow Poop: Cow’s Milk or Something Else?

Stool Changes due to Introducing Cow’s Milk

Since introducing cow’s milk is the only change you have done to her diet, I would definitely take it out of her diet again and see if there is an improvement.

It is very possible that her loose stools, irritability, and the smell and color of her stools are all related to either lactose intolerance or milk protein allergy.

The color of her stools is not necessarily an issue, unless it is chalky pale yellow. But you describe the color as similar to breastmilk poop, which shouldn’t be a problem. Even if it is related to the cow’s milk, the color alone is probably nothing to worry about.

I haven’t been able to find any research that supports the idea that the poop color can change to yellow when introducing cow’s milk. However, a quick search on Google make a substiatial amount of forum posts with similar questions pop up.

However, diarrhea and loose stools (for any reason) are often relatively yellow, simply because they travel faster throught the digestive system. So it is possible that for those babies that get loose stools from the cow’s milk introduction, also simply have more yellowish poop for that reason. Not because of something in the milk, but because the baby is sensitive to cow’s milk, gets some degree of diarrhea, and thereby more yellowish stools. I don’t know if this could be the reason, but facts remain that I can’t find any research that supports yellow stools from cow’s milk.

In any case, unless you notice other signs of illness (such as a fever or vomiting), take her off dairy products – either all dairy or start with experimenting with lactose-free products. At the same time, schedule an appointment with her health care provider to discuss if you should test her for lactose intolerance or milk allergy or if you should simply introduce the milk more slowly.


It is, of course, possible, that your toddler has loose, foul-smelling stools for other reasons than the cow’s milk introduction. Just because some things happens at the same time, they are not necessarily related.

A possible cause of all your baby’s symptoms, including yellow stools, is Giardiasis. This disease is caused by a parasite. It is a very common cause or diarrhea, especially among children. I many cases, no treatment is needed, but if the symptoms persist, there is medicin available.

Giardiasis is diagnosed through a stool sample.

To conclude, I can’t, of course, say what is the reason for your baby’s yellow, loose stools. Sensitivity to cow’s milk or Giardiasis are definitely two options to investige.

I’ll include a few links about babies with similar issues below.

Good luck!

Babies With Cow’s Milk Issues

Find comments to this question below.

Comments for “1 Year Old Yellow Stool, Cow’s Milk?”

Sep 04, 2018cows milk, bad diaper rash, green stools

by: Anonymous

Hi, my 1 yr old son just started drinking cows milk. It seemed fine at first but started to notice a color change in stools really bad diaper rash. More like a dark green or light green stools and very runny.

Feb 01, 2019addressing green stools

by: Anonymous

My 13-month-old just had a stomach virus and green stools and her dr said that the green is bile in the stools :( He kept her on a normal diet just minus the cheese, and lactose-free milk (they do make whole milk Lactaid) instead of regular whole milk.

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