Poop Changes When Transitioning to Whole Milk: What To Expect

| Reviewed By Sarah Schulze, MSN, APRN, CPNP

It’s no secret that mothers see a lot of poop every day. We see it so often, in fact, that we notice when there is something different or off about it. That, in turn, makes our baby’s poop one of our biggest concerns.

It’s just one of the many joys of motherhood! 

If your little one just recently transitioned to cow’s milk, you may have noticed some changes in their stool. Any change in your baby’s poop can be concerning, especially for new moms!

Rest assured, however, that your baby’s poop will undergo some normal changes throughout the transition process. They are, after all, changing their diet, which will affect their stool. 

Let’s take a look at some of the things you can expect to see in your little one’s diaper over the next few weeks as they consume more whole milk. We will also discuss the warning signs and indicators of more serious problems. 

Normal Changes

You should expect your little one’s poop to look a little different during the first few weeks of transitioning to cow’s milk. As you scroll, you will find a breakdown of the common reactions and why they happen.

1. Poop Harder Than Normal

Initially, whole cow’s milk may cause your baby’s stool to be harder than normal, and it may even cause a bit of constipation.

This is likely because your little one’s digestive system is still getting used to the new proteins in cow’s milk. Try not to give your baby more than 24 ounces of whole milk a day, and incorporate plenty of water and fiber in their diet. 

2. Softer Poop

On the other hand, introducing cow’s milk could also cause your baby’s poop to be softer than usual.

Because they are ingesting more lactose than they are used to, during the first few days they may pass more stools that seem looser than normal.

If this happens, try easing the transition a bit more by mixing the milk with formula or offering slightly more every couple of days. 

Diarrhea, however, could be a sign of serious illness or lactose intolerance. If it lasts more than a few days and, especially, if it is accompanied by other symptoms such as fever, bloating or gas, contact your pediatrician.

3. Lighter Colored Poop

Noticing color changes in your baby’s stool after introducing cow’s milk is also completely normal.

The color of stool is a reflection of their diet and what they consume, so it makes sense that it would change when introducing something new. 

As you transition to whole milk, your baby’s poop may become light brown or tan. Tan or caramel-colored stool should not be a cause for concern. 

4. Small, White Specks in Stool

There are two protein groups in milk: whey proteins and casein.

Cow’s milk has much more casein than human milk or baby formulas. When these proteins are exposed to the acid in your little one’s stomach, they have different reactions.

Whey protein forms soft, easy-to-digest curds that usually pass through the digestive system without problems. Casein, however, forms hard curds that are more difficult to digest.

As a result, you may see small, white specks in your baby’s stool when they first transition to whole milk. This is from the undigested casein proteins. 

5. More Frequent Bowel Movements

During the first few weeks of the transition, your baby may seem to be filling up the diapers a lot more frequently than they did before, and they are probably way smellier too!

These are both common initial reactions to cow’s milk. Give it a few weeks, and see if your little one’s digestive system gets the hang of things. The frequency should go back to normal. 

If your little one continues to have frequent, loose bowel movements even after a few weeks, you may want to contact your pediatrician. Your little one could be lactose intolerant or have a sensitivity to the protein in cow’s milk. 

6. Bowel Movements Less Frequently

Less frequent bowel movements could also be a symptom during the transition. Every baby’s body reacts differently!

Babies can go from pooping after every feeding to only once or twice a day. Some may even go every other day.

Less frequent bowel movements could just mean that your baby’s digestive system is learning how to process cow’s milk. 

If your baby becomes severely constipated, experiences pain during a bowel movement, or is passing pebble-like stools, contact your pediatrician. 

A cute toddler in a diaper holding up one of his legs.

Abnormal Changes

While some changes in your little one’s poop are normal during the transition to milk, there are some things to look out for.

Some reactions are not normal and can be an indication that there is something else going on instead of normal digestion adaptation.

1. Severe Constipation

Yes, your little one’s stools may become a little harder than normal, but severe constipation is a warning sign that the milk is causing an undesired reaction in your baby’s belly.

If you notice your little one struggling to pass stool, not having a bowel movement in several days, or passing small, pellet-like stool, you need to contact your pediatrician. 

2. Severe Diarrhea

Severe diarrhea after being introduced to milk can be an indicator of lactose intolerance. This means that your baby’s small intestine does not make enough lactase, which is the enzyme used to break down lactose.

If you are cleaning up a diarrhea blowout several times a day and it seems to be lasting a while, you may need to stop giving your little one milk and speak with your pediatrician to discuss lactose-free options. 

Diarrhea is also a common symptom of many illnesses in babies. If your child’s diarrhea is accompanied by a fever, nausea, or any other symptoms, take him to the doctor to determine the root cause and receive proper treatment. 

3. Black Stool

A baby’s very first few bowel movements will be black. This is called meconium and is normal. However, after the first week or so of life, your baby should not have black poop again!

If they do, it is usually a sign of something serious such as gastrointestinal bleeding. If your little one has black stool, it is always a good idea to call your pediatrician. 

4. Blood in Stool

A lot of times, blood in stool after transitioning to cow’s milk for the first time is a sign of a cow’s milk protein intolerance. If you notice streaks or flecks of blood in your baby’s poop, stop giving him milk, and see if it goes away.

If it doesn’t, your baby should be seen by a pediatrician to rule out any other serious illnesses that could cause blood in stool. 

5. White, Gray, or Very Pale Poop

If your baby has chalky white, gray, or very pale poop, seek medical attention right away.

The most common cause for pale poop is a blockage in the liver that prevents it from releasing bile, the green fluid that gives stool its yellow/ brown color.

Another cause for gray poop could be malabsorption, meaning your baby’s body is not absorbing the nutrients from food as it should. Both are very serious and need immediate medical treatment. 

6. Mucus in Stool

A small amount of mucus in your baby’s stool is not a cause for concern.

However, large amounts of mucus, mucus in several stools in a row, or mucus accompanied with diarrhea and other symptoms could point to an allergy, gastrointestinal infection, or other problems. 

Signs of Milk Allergy in 1-Year-Old

A milk allergy occurs when your little one’s immune system mistakenly recognizes cow’s milk protein as a foreign invader and releases histamine to combat it.

The histamine causes reactions in your baby that let us know he has a milk allergy. The signs include: 

  • Hives and mild to severe swelling 
  • Difficulty breathing, wheezing, coughing 
  • Itchy or red eyes 
  • Tightness in the throat 
  • Repeated vomiting or diarrhea 
  • Congestion, copious clear discharge, sneezing 
  • Change in behavior or mood
  • Dizziness 
  • Drop in blood pressure

Children who have a milk allergy will begin showing symptoms immediately within 2 minutes and up to two hours of consuming the milk product.

A milk allergy is pretty rare and only affects 2.5% of children under the age of three, and most children will outgrow this allergy. 

It is important to note the difference between a milk allergy and a sensitivity such as lactose intolerance.

Lactose intolerance has more to do with your child’s GI tract and the inability to break down lactose. This usually causes symptoms such as diarrhea, nausea, cramps, gas, and bloating, which are similar to allergy symptoms.

The best method for determining if your baby is allergic or lactose intolerant is to have your pediatrician test for allergens. 

Switching Baby To Whole Milk – Best Practices

As your baby’s first birthday approaches, you may be wondering how the transition from breastmilk or formula to cow’s milk will go for your little one. Will they like it? Will it hurt their stomach? How will it affect them?

There are a few different ways that you can make the switch to whole milk, and which one you choose really depends on your baby! 

In the beginning, I would always recommend trying a little bit, meaning a few ounces at a time, just to make sure your baby will not have any kind of negative reaction to the milk.

After this initial “test,” there are a few different methods you could follow to complete the transition. 

It should also be noted that children do not HAVE to switch to cow’s milk at all.

Breastfeeding is recommended by WHO for at least 2 years, so if you and your baby are still happily breastfeeding, there is no reason to switch to cow’s milk at all. You can offer water with meals or even breastmilk in a cup.

For formula-fed babies, formula is no longer nutritionally necessary around 12 months of age (including “toddler formula”) and can be discontinued.

Water can be given at meals, and if you want to offer cow’s milk, you definitely can, but it is not a necessity.

Calcium and vitamin D requirements can be met through other dairy foods, such as cheese and yogurt, if desired or if your child doesn’t like cow’s milk. 

Cold Turkey

Some babies are just fine transitioning straight to whole milk. They don’t seem to mind the taste difference at all.

If this is the case and you do not notice any negative reactions to the milk, you may cut formula or breastmilk cold turkey after their first birthday and move right on to whole milk. 


Many babies are not too keen on the taste difference at first, and the transition may be a little more difficult. In this situation, try mixing whole milk with breastmilk or formula.

Gradually decrease the amount of formula/breast milk every few days until you can make the full transition. 


Your little one’s poop is the best indicator of their overall health. It is good to be worried about it!

Hopefully, you have a little more insight now into the stool changes that you should and should not see as your toddler begins consuming cow’s milk.

If you are still worried or concerned, do not hesitate to call your pediatrician! You can never be too safe when it comes to your little one’s health!