Poop Changes When Switching to Whole Milk: What To Expect

| Reviewed By Sarah Schulze, MSN, APRN, CPNP

If a baby is transitioning to whole milk, it is normal for their stool to go through changes, such as:

  • Harder or softer than normal
  • Lighter in color
  • Small white specks in stool
  • Bowel movements more or less frequent than normal

Abnormal changes include:

  • Severe diarrhea or constipation
  • Black stool or blood in stool
  • Stool very pale in color
  • Mucus in stool

Your baby’s poop will undergo some normal changes throughout the transition process.

However, according to Healthline:

It’s always a good idea to keep an eye on your baby for the first week or so after making the switch. Look for:

  • Irritability
  • Excess gas
  • Diarrhea
  • Vomiting
  • Skin rashes

One of my children adjusted to whole milk without any noticeable changes, but the other one experienced very loose stools for the first few weeks of the transition.

Every child is unique!

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, they may pass more stools that seem looser than normal in the first few days of the switch.

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 diarrhea lasts more than a few days and 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 formula. 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, 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 the 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 by diarrhea and other symptoms could point to an allergy, gastrointestinal infection, or other problems. 

Human Breast Milk vs. Cow’s Milk

NutrientHuman MilkCow’s Milk
WaterAbout 87%About 87%
FatAbout 4.4%About 3.6%
ProteinAbout 1%About 3.2%
CarbohydratesAbout 7.0%About 4.7%

How Much Milk Should a 1-Year-Old Drink?

The American Academy of Pediatrics (AAP) suggests that children between the ages of 1 and 2 years should consume whole milk to support their growth and brain development.

The general guideline is to aim for about 16 to 24 ounces (480 to 720 milliliters) of whole milk per day for a one-year-old.

This can be spread out over the course of the day, typically divided into two or three servings.

Remember that this is a rough guideline. Some children may naturally consume more or less milk based on their appetite and dietary preferences.

Additionally, it’s crucial to consider the child’s overall diet.

Milk should complement a balanced diet that includes a variety of foods from all food groups.

Switching Baby To Whole Milk – Best Practices

As your baby’s first birthday approaches, you may be wondering how the transition from breast milk 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 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. 

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 breast milk cold turkey after your child’s 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 breast milk or formula.

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


Breastfed babies and many formula-fed babies are used to warm milk, and they might not enjoy whole milk straight from the fridge.

Try warming the milk gently before offering it to your little one.

Make It Fun!

Try introducing whole milk in a sippy cup adorned with your child’s favorite characters.

This is such a “big kid” treat that your baby might not even notice the switch to whole milk, and at 12 months old, it’s time to say goodbye to bottles anyway!

Skip the Switch!

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 breast milk 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. 

Lactose Intolerance in Babies

Lactose intolerance in babies occurs when a baby has difficulty digesting lactose, a sugar found in milk and dairy products. 

This happens due to a deficiency of an enzyme called lactase, which is responsible for breaking down lactose into simpler sugars that can be absorbed by the body.

Lactose intolerance in infants is relatively rare compared to lactose intolerance in older children and adults.

Most babies are born with enough lactase to digest breast milk or formula, which are their primary sources of nutrition.


There are two main types of lactose intolerance in babies:

  • Primary lactose intolerance: This is a genetic condition where a baby is born with low lactase levels. This is more common in certain ethnic groups, such as people of Asian, African, Hispanic, or Native American descent.
  • Secondary lactose intolerance: This is a temporary form of lactose intolerance that can develop after an illness, particularly a gastrointestinal infection. It occurs because the lining of the intestines is temporarily damaged, reducing the production of lactase.


Common symptoms of lactose intolerance in babies include:

  • Diarrhea
  • Bloating
  • Gas
  • Stomach cramps or pain
  • Irritability
  • Fussiness during or after feedings
  • Excessive crying
  • Redness around the baby’s mouth


If you suspect your baby may have lactose intolerance, it’s important to consult a pediatrician.

They will typically perform one or more of the following tests:

  • Hydrogen breath test: This measures the amount of hydrogen in the breath after the baby drinks a lactose solution.
  • Stool pH test: This checks the acidity of the baby’s stools after consuming lactose.
  • Elimination diet: This involves removing lactose from the baby’s diet to see if symptoms improve.


The treatment for lactose intolerance in babies depends on the severity and type of lactose intolerance:

  • Breastfeeding: For lactose-intolerant babies, breastfeeding is generally well-tolerated. In some cases, the mother may need to adjust her diet to reduce lactose intake.
  • Lactose-free or lactose-reduced formula: If a baby is formula-fed, there are specialized lactose-free formulas available. These are typically made from soy protein or other non-dairy sources.
  • Supplemental lactase drops: Some babies may benefit from lactase enzyme drops, which can be added to breast milk or formula to help break down lactose.
  • Diet modification (for older infants): As a baby grows and starts eating solid foods, parents can gradually introduce lactose-containing foods and monitor for symptoms.


With proper management and adjustments to the baby’s diet, most infants with lactose intolerance can lead normal, healthy lives.

It’s important to work closely with a healthcare provider to ensure the baby receives appropriate nutrition and care.

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. 

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