The Crying That Won't Stop: What New Science Says About Colic and Your Baby's Gut

It's 2 a.m. You've fed them. Changed them. Rocked them. Sang every lullaby you know and a few you made up. And still, they're crying.

If you're living through colic right now, you already know it's one of the hardest things about new parenthood. What you may not know is that researchers are finally starting to understand why some babies cry like this. The answer may have less to do with anything you're doing, and more to do with what's happening inside your baby's gut.

So What Is Colic, Really?

Doctors define colic by the "rule of threes": crying more than three hours a day, more than three days a week, for more than three weeks, in a baby who's otherwise healthy.

It affects about 1 in 5 babies. And for decades, the standard advice has been some version of "hang in there, it'll pass." Helpful? Not really.

But here's what's changed. Scientists have been comparing the gut bacteria of colicky babies to non-colicky babies, and a clear pattern keeps showing up. Babies who cry inconsolably tend to be missing something specific in their guts: a family of bacteria called Bifidobacterium^2,3.

Why a Baby's Gut Is Basically Mission Control

In the first weeks of life, your baby's gut isn't just digesting milk. It's helping build their immune system, train their nervous system, and set the foundation for lifelong health¹.

The star players in all of this? Bifidobacterium, especially strains like B. infantis and B. breve. These bacteria are uniquely designed to break down the special sugars in breast milk, and as they do, they produce compounds that calm inflammation and create a stable, comfortable gut environment¹.

When those bacteria are missing, less helpful bacteria can move in. The result can be a gut that's gassy, inflamed, and uncomfortable, and a baby who has no way to tell you any of that except by crying.

The Surprising Reason Most Babies Are Starting Out Short

Here's the part that surprises most parents: the majority of American babies are missing these key bacteria from day one.

In the largest study of its kind in the U.S., researchers analyzed the gut microbiomes of 412 infants across 48 states. The findings:

• 90% were missing one or more key strains of Bifidobacterium⁴

• 1 in 4 had none detectable at all ⁴

This isn't anyone's fault. It's the result of decades of changes in how we give birth, feed babies, and use antibiotics. C-sections, antibiotics during labor, and formula feeding can all interrupt the natural transfer of these microbes from mother to baby. None of those things make you a worse parent. They're just realities of modern medicine, and they have real biological ripple effects.

In parts of the world where birth and feeding look more like they did a century ago, this transfer still happens reliably. In the U.S., it often doesn't.

What This Means for You

Supporting your baby's microbiome won't solve every case of colic, and the research is still evolving. But given how consistently the science links low Bifidobacterium to colicky babies, giving your baby's gut the bacteria it needs is one of the most grounded, evidence-based things you can do in those early weeks.

That's where Persephone comes in. Our infant probiotic is designed to deliver the specific strains of Bifidobacterium that modern birth and feeding practices can interrupt, the same strains the latest science points to as essential for early gut health.

It won't make every hard night easy. But it's one of the most evidence-based things you can do to give your baby's gut what it's been quietly missing.

And to every exhausted parent reading this at 2 a.m., you're not failing. You're paying attention. That already makes you a great parent.

Medical Disclaimer: The information provided on this blog is for educational purposes only and is not intended as medical advice, diagnosis, or treatment. Every baby is unique, and health decisions should always be made in partnership with a qualified healthcare professional. If you have questions or concerns about your child's health, diet, or development, please consult your pediatrician or another trusted healthcare provider before making changes.

Sources

1. Henrick, B. M., et al. (2021). Bifidobacteria-mediated immune system imprinting early in life. Cell, 184(15), 3884–3898.e11. https://doi.org/10.1016/j.cell.2021.05.030
   
   

2. Indrio, F., et al. (2020). Colic and the infant microbiome. Expert Review of Gastroenterology and Hepatology. https://doi.org/10.1080/17474124.2020.1791702
   
   

3. Mu, S., et al. (2023). Bifidobacterium and infantile colic. Scientific Reports. https://doi.org/10.1038/s41598-023-36641-z
   

4. Jarman, J. B., Torres, P. J., Stromberg, S., et al. (2025). Bifidobacterium deficit in United States infants drives prevalent gut dysbiosis. Communications Biology, 8, 867. https://doi.org/10.1038/s42003-025-08274-7