For many exhausted parents, the promise of a full night’s sleep from “cry it out” methods can sound like a lifeline. But research into infant development and nervous system health suggests this approach may carry unintended consequences. Understanding how babies are wired for connection helps us see why biologically responsive care can support not only sleep but also lifelong emotional wellbeing.
What is “Crying It Out”?
“Crying it out” (CIO) is a term often used for sleep training methods where babies are left to cry for set periods without parental comfort, in the hope they will learn to self-soothe and fall asleep independently. While it’s been promoted as a quick fix for sleepless nights, this approach doesn’t align with how an infant’s brain and nervous system develop.
The Biology of Connection
Human babies are born neurologically immature. Their brains and nervous systems are still under construction, especially the areas that regulate stress and emotion. When a baby cries, it is their only way of signalling a need—whether for food, warmth, comfort, or reassurance. From a biological perspective, a caregiver’s responsive touch, voice, and presence help regulate the baby’s stress response system, teaching them that the world is safe and their needs will be met.
When caregivers respond consistently, it builds secure attachment. This doesn’t mean babies will never cry, but that their distress is met with comfort, which in turn helps their nervous system learn how to calm down over time.
What Happens With “Crying It Out”?
During prolonged periods of crying without comfort, a baby’s body produces stress hormones like cortisol. In the short term, this can leave them in a state of “fight or flight” (increased heart rate, rapid breathing, and distress). Over time, if a baby repeatedly finds their cries unanswered, they may stop crying—not because they’ve learned to self-soothe, but because their nervous system has shifted into a “freeze” state, conserving energy by shutting down their cues.
This can be misinterpreted as success, but research suggests the baby’s stress physiology remains elevated even after they fall silent. Chronic high cortisol levels in early life are linked to changes in brain architecture, affecting areas like the amygdala and hippocampus which are vital for emotional regulation and memory.
Biologically Responsive Care: A Protective Alternative
Biologically responsive care, sometimes called “responsive parenting” is about meeting a baby’s needs promptly and with sensitivity. This approach helps regulate their nervous system and strengthens the pathways that support emotional resilience. Instead of teaching a baby to sleep through separation, it nurtures the developmental processes they need to eventually regulate their own sleep.
This doesn’t mean parents must be perfect. Babies benefit most from “good enough” care and consistent, loving responses most of the time. Sleep challenges are common and temporary, but the foundations for lifelong mental health and connection are built in these early months. Lyndsey Hookway is a great source of information on Holistic Sleep Coaching.
The Bottom Line
Crying is communication, not manipulation. While sleep training may promise results, it’s important to weigh these against the needs of a rapidly developing brain. Responding to your baby’s cries may take longer in the short term but can foster secure attachment, healthier stress regulation, and a calmer nervous system for years to come.
