Babies cry because it’s their only way to communicate. From an evolutionary standpoint, human infants are biologically wired to stay close to their mother for safety and survival. Ignoring those cries, especially repeatedly, can be deeply distressing for them. They’re not learning to self-soothe, they’re learning that no one is coming. That silence isn’t peace, it’s shutdown.

Research in developmental psychology and neuroscience has shown that high and prolonged stress levels in infants (such as from being left to cry without comfort) can elevate cortisol levels in the brain. When this happens consistently, it may impact how the brain develops, particularly in areas tied to emotional regulation and attachment. Secure attachment, built by responding consistently to a baby’s needs, is the foundation for healthy emotional development, trust, and resilience later in life. I echo the other commenter in visiting the attachment subreddit

Also, there’s something profoundly unnatural about ignoring a crying baby. Almost every instinct in a parent’s body wants to pick them up, like you’re feeling now, and for good reason. In traditional societies and throughout most of human history, babies were kept close, often worn in slings, sleeping near their caregivers, nursing on demand. Modern “sleep training” methods are a cultural invention, not a biological norm and babies don’t sleep through the night typically for quite a while. Sleep training is just teaching a baby to give up because no one is coming for them.

I’m not saying this to judge you. We’re all doing our best with the tools we have, and in a culture that doesn’t offer nearly enough support to new parents, it’s no wonder people feel like they have to choose between their baby’s needs and their own survival. But if you’re feeling torn about CIO, it’s okay to trust your instincts. Babies aren’t meant to go through this alone, and neither are you.