Getting spit up on your shirt is practically a right of passage for becoming a parent, but if your baby throws up curdled milk, you may wonder what is going on. As it turns out, throwing up curdled milk could be completely normal — it all has to do with how much time has passed since your baby nursed [1] or took a bottle. We reached out to two pediatricians to learn more about why spit up might resemble milk left in the fridge past the expiration date and when to worry about it.

What Does It Mean When My Baby Throws Up Curdled Milk?

"Curdled milk is the result of milk mixing with stomach acid," said Ohio-based ob-gyn Kim Langdon, MD [2]. When the milk in your refrigerator gets old, its pH drops making it more acidic. In your baby's stomach, digestive acids have the same effect. Dr. Langdon explained that the longer the milk remains in the stomach before the baby spits it up, the more curdled it looks.

Should I Be Worried About Curdled Spit Up?

"[Spitting up] is not a sign of illness," said Pierrette Mimi Poinsett, MD [3]. "All babies have a degree of reflux resulting in throwing up milk."

"Spitting up is common and usually occurs with burping the baby," Dr. Langdon told POPSUGAR, noting that while this is completely normal, vomiting is not. Vomiting can be hard to differentiate from spit up, but it generally comes up more forcefully and in larger amounts. Repeated vomiting could be a sign that your baby has a virus and can lead to dehydration. If you think your baby is vomiting or you are concerned about the frequency of spit up, Dr. Langdon advised reaching out to your pediatrician.

How Can I Reduce My Baby's Spit Up?

Although spitting up is completely normal in infants, you may want to take steps to reduce it if it's making your baby uncomfortable or preventing them from taking in enough milk. "To reduce the amount of vomited milk, you can feed the baby more slowly, taking more breaks in the feeding," Dr. Poinsett told POPSUGAR. She also suggested using a slow-flow nipple for bottle-fed babies and burping your baby halfway through the feeding, as well as at the end of the feeding.