Is breastfed baby poop acidic?

The normal poop of a breastfeeding infant is yellow, seedy and runny. Occasionally, babies pass blackish stools with a tar-like consistency called meconium.

Foul-smelling baby poop can indicate a variety of issues, from food sensitivities to medical problems. Most of these issues are easy to prevent, like avoiding foods that are too acidic.


1. Lactose Overdose

Lactose is a sugar found in milk, and it is digested by the enzyme lactase (lactase is also made as a supplement). Newborn babies may sometimes have lactase deficiency at birth. But this is rare, and most of these babies will be able to digest milk after they are born.

If a breastfed baby eats too much milk at once, the stomach cannot process it all. So the undigested lactose is pushed into the large intestine. Intestinal bacteria normally present in the bowels then ferment this undigested lactose into gas. This causes bloating, intestinal cramps, and watery or sloppy stools (also known as flatus). These bowel movements are acidic and cause pain/discomfort for the baby.

Babies with lactose overload can be fussy and have more wet nappies than normal in 24 hours. They can also have green, frothy, or explosive poop. This is an example of a homeostatic mechanism to prevent too many calories from being taken in at once.

Orange poop in a breastfed baby could mean they are getting too much foremilk (the less fatty part of the milk) and not enough hindmilk, Swanson says. However, if the baby is vomiting or has blood mixed into the stool, call your pediatrician immediately. This indicates a more serious problem. Also, if the baby has been taking antacid or acid-suppressing medication recently, the doctor will want to do a hydrogen breath test to check for lactose intolerance (this is because these types of medications delay gastric emptying). Taking lactase supplements can help babies with lactose intolerance break down dairy sugar more quickly.

2. Food Allergies

For the first few days after birth, a newborn passes thick, blackish stools with a tar-like consistency. This is known as stool meconium and is perfectly normal. After the meconium has passed, your baby’s poop will be mustard yellow to yellow-green in color and seedy or mushy. This is also perfectly normal, especially if your baby is breastfed.

When your baby starts eating solid foods, their poop will be greener or more tan in color and may contain small white seeds. As your baby gets older, their poop will become thicker and more peanut butter-like in consistency as they add more solids to their diet.

If you notice your baby’s poop changing in color or texture, it’s important to talk to your doctor about it. This can be a sign of an allergy to a food or an imbalance between foremilk and hindmilk caused by switching from one breast to another during breastfeeding sessions.

It’s a good idea to eliminate the suspected allergen from your baby’s diet (with the help of your GP) to see if symptoms improve. Then, slowly reintroduce the food to make sure your baby isn’t allergic to it. It’s important to eat a balanced diet during this process so that you can determine which foods your baby is truly sensitive to. Talk to our Happy Baby Experts for more information and support.

3. Intestinal Infections

If a baby is eating a food they are sensitive to, their digestive system can get an infection and that can show up in the form of acidic poop. This is usually accompanied by a red and angry nappy rash that looks like a bleeding wound.

Sometimes mucus will be present in your baby’s poop, and it can look jelly-like with shiny glistening strings. This can occur when a baby is especially droopy because the drool tends to go undigested and ends up in their stool.

The intestines secrete mucus to help stool pass more effectively through them. Mucus in poop isn’t always something to worry about, but it can be a sign of a milk allergy or a bacterial infection such as cystic fibrosis.

Researchers have found a link between a healthy gut microbiome and stool pH, particularly for infants. It is believed that a particular species of bacteria called Bifidobacterium, specifically B. longum subsp. infantis, helps to lower stool pH by metabolizing human milk oligosaccharides into acidic end products like lactate and acetate. When a baby lacks this type of bacteria in their intestinal microbiome, they produce dirty diapers with higher pH. In addition, these babies have a more abundant load of potentially virulent pathogens and exhibit chronic enteric inflammation.

4. Dehydration

Most babies will poop two to five times a day, with each bowel movement being different in color and consistency. Most breastfed infant poo is soft and watery and sometimes contains curds that look like mustard or seed-like particles (Wambach and Spencer, 2020). The smell of a baby’s poop is usually mild, although some parents say it has a sweet or yeasty odor.

Acidic poop occurs when the unabsorbed lactose in breast milk is converted into lactic acid. This lowers the poop’s pH and can cause diaper rash. Food allergies, especially to dairy products, can also cause acidic poop. Foods containing high amounts of fructose, such as apples, oranges, bananas, pineapples, and pears, are also known to make poop more acidic.

If your child is exhibiting signs of dehydration, such as no urine in the diaper for more than eight hours, dark yellow or brown urine, dry tongue, and lips, and slow blood refill test (press on the thumbnail and watch for how long it takes to turn pink), see a doctor immediately. Severe dehydration will be accompanied by rapid breathing and a weak but rapid pulse.

In addition to these symptoms, dehydration in young babies can also cause a fever and irritability. A baby may become irritable and fussy when he is unable to get enough fluids to be satisfied.


Breastfed baby poop is often described as having a mustard-yellow or golden color and a loose, seedy consistency. Its acidity is a normal and healthy characteristic of breastfed infant stool. However, it’s important to note that the acidity level is generally mild and not harmful to the baby.As a baby’s diet changes, such as when they start to consume solid foods, the composition and characteristics of their stool may also change. If you have concerns about your baby’s stool or digestive health, it’s advisable to consult with a pediatrician or healthcare provider for guidance and reassurance.

Why is breastfed baby poop acidic?

Breast milk is naturally slightly acidic, and this acidity helps maintain a healthy environment in the baby’s digestive system. It also plays a role in preventing the growth of harmful bacteria in the infant’s gut.

What does breastfed baby poop look like?

Breastfed baby poop typically has a mustard-yellow or golden color and a loose, seedy consistency. Its appearance can vary somewhat from one baby to another, but it’s generally similar in texture and color.

Is acidic breastfed baby poop a cause for concern?

No, the mild acidity of breastfed baby poop is entirely normal and not a cause for concern. It’s a sign that the baby’s digestive system is functioning as it should. However, if you notice any significant changes in the color, consistency, or frequency of your baby’s stool, it’s a good idea to consult with a pediatrician.

Does the acidity of breastfed baby poop change as the baby grows?

The acidity level of breastfed baby poop remains relatively stable throughout the breastfeeding period. However, as a baby’s diet changes when they start consuming solid foods, the characteristics of their stool may also change.

How can I tell if my baby’s poop is too acidic or if there’s a problem with their digestion?

Generally, mild acidity in breastfed baby poop is not a cause for concern. If you’re worried about your baby’s stool or suspect a digestion issue, it’s best to consult with a pediatrician or healthcare provider. They can provide guidance and address any concerns you may have.

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