Loose, mucousy, or blood-tinged stool could indicate a cow’s milk protein allergy in babies. Here’s how to spot the symptoms. 

By Nicole Harris
May 27, 2021
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New parents soon learn that baby poop comes in all shapes, textures, and colors. Breastfed babies usually have seedy mustard-colored poop, while formula-fed infants have firmer yellow or brown poop. And while a temporary change in color or texture usually isn't anything to worry about, irregular bowel movements can sometimes indicate a food intolerance.

According to Wendy Sue Swanson, M.D., MBE, FAAP, pediatrician and Chief Medical Officer of SpoonfulONE, food sensitivities aren't too common in babies, but they show up occasionally. One of the major culprits is cow's milk—specifically the protein molecules in the dairy product, which can trigger an overreaction of the immune system. Formula-fed babies might have sensitivity to the cow's milk in their formula. Breastfed babies, on the other hand, can react to cow's milk particles that "leak" into their bloodstream in small quantities after nursing. 

diaper change technique
Credit: Liderina/Shutterstock 

Here's what you need to know about the link between baby poop changes and milk protein allergies, with tips for relieving your baby's gastrointestinal symptoms. 

Baby Poop and Milk Protein Allergies

If your baby has a cow milk's protein intolerance, you might notice some telltale symptoms: irritability, abdominal pain, vomiting, sore bottom, and rashes. What's inside their diaper could also be a major clue. Here's what to look for:

  • Looser and mushier stool (diarrhea), especially if it happens two to four times per day for more than 5-7 days
  • Poop tinged with a small amount of blood. “Bright red can show an inflammation of the colon,” says Dr. Swanson. 
  • Mucousy stool that resembles snot in the diaper

Note that babies could also have a true milk allergy instead of a cow milk's protein intolerance, although it's more rare. Symptoms appear immediately and include hives, wheezing, and vomiting.

What to Do for Milk Protein Allergies

Does your baby's poop look loose, mushy, blood-streaked, or mucousy? They might have a sensitivity to cow's milk protein. Your pediatrician will probably recommend an elimination diet, which involves removing triggering foods from Mom's plate (milk, cheese, yogurt, ice cream, etc.). Formula-fed babies might switch to a different type of formula. Symptoms should improve within two or three weeks.

Although unusual baby poop can seem alarming, experts stress that minor intestinal inflammation isn't a big deal, and your pediatrician will likely recommend re-introducing your baby to dairy at some point. Most children grow out of cow's milk protein allergies by the time they turn 5 years old. (Note that a cow's milk protein allergy isn't the same thing as lactose intolerance or true milk allergies.)