The health visitor stood with her back against the door literally blocking it so I could not get to my crying baby. At the time of this visit, my daughter had been crying almost constantly since birth, not out of hunger or illness, but because she simply needed to be held and comforted. We were both utterly exhausted, having been through a 36-hour breech labour and then nearly a full week with very little rest. The health visitor, however, was firmly of the “cry-it-out” school of thought. I was young, impressionable and completely worn down, so I listened to her advice, even though every instinct in my body told me otherwise.
I initially followed her advice but felt as though a knife was searing through my body. After a few minutes my daughter’s cries changed and I could tell she was in real distress. “You have to see it through now!”, advised the midwife. “Otherwise she will know she can get her own way. My daughter was six days old.
At once, my husband and I made for the door and, fixing the midwife with a steely glare, I advised her politely but firmly to get out of our way. I picked my daughter up and from that moment onwards, one or other of us carried her constantly. Not long afterwards, someone gave me a book called The Continuum Concept by Jean Liedloff. That book didn’t just change the way I parented, it started me on a journey to understand the neuroscience of attachment and the real effects of our caregiving choices in those early weeks and months.
The idea that babies should be left to cry themselves to sleep is relatively new. For most of human history, babies slept close to caregivers, waking often and being responded to throughout the night. This was not seen as a problem to fix, but as a normal part of caring for an infant whose nervous system is still developing.
The cry-it-out method (CIO) emerged in the early twentieth century, alongside the rise of behaviourist psychology and increasingly rigid childcare advice. Influential voices of the time such as Dr. Luther Emmett Holt, who advocated letting babies cry to strengthen lungs, Dr. Richard Ferber, who introduced timed checks, and Marc Weissbluth who developed the stricter "extinction" approach, all falling under the broader CIO umbrella.
The cry-it-out method encouraged parents to avoid responding too quickly to crying, warning that too much comfort would create dependence. As industrialisation and modern work patterns took hold, families became more isolated, support networks thinned, and uninterrupted adult sleep became harder to sacrifice. Methods that promised babies could be trained to fit adult schedules began to feel not just appealing, but necessary.
Over time, cry-it-out has been absorbed into mainstream parenting culture. Night waking has become a “sleep problem,” and infant independence is often treated as an early developmental goal.
Sleep training methods have become increasingly popular to sleep-deprived new parents in a society which places the highest value on their productivity in the workplace. According to the Ramos & Youngclarke (2006) study of popular U.S. parenting books about infant sleep, about 60 % of the books reviewed endorsed “cry-it-out” or controlled-crying-style sleep training techniques.
So is the CIO method a useful approach to allowing both you and your baby to get a better night’s sleep, or are there hidden costs?
Short-term studies on cry-it-out often show small changes, but they’re not as dramatic as they’re sometimes made to sound.
One well-known study from Flinders University found that after three months, babies who were left to cry fell asleep around 15 minutes faster than babies who weren’t sleep trained, while babies supported with a gentler “bedtime fading” approach settled about 12 minutes faster.
What’s telling is that when the same families were checked a year later, all the babies were sleeping for similar lengths of time. In other words, sleep improved as babies got older, regardless of the method used, raising the question of whether those early gains would have happened anyway.
Long-term studies are often used to reassure parents that cry-it-out is safe, and on the surface, they do offer some comfort. Research following children for up to five years has generally found no clear differences in attachment, emotional wellbeing, or behaviour between children who were sleep trained and those who weren’t. Follow-ups at 18 months, three years and five years suggest that, in most cases, cry-it-out doesn’t lead to obvious long-term harm, and some studies even link sleep training with reduced parental depression.
That said, these findings don’t completely settle the debate. Many of these studies rely on parent reports rather than measuring what’s happening in a baby’s body during distress, and “no difference” years later doesn’t tell us much about how stress was experienced in the moment. Even researchers who find no harm tend to stress context: children raised in generally responsive, loving environments are likely to be resilient to short-term stress, but that doesn’t mean every baby experiences cry-it-out in the same way. There is also very little research looking at: stress reactivity later in childhood, emotional regulation under pressure or the differences between sensitive vs less sensitive infants.
For many parents, that uncertainty, rather than clear evidence of damage, is a concern.
When a baby cries and no one comes, their body experiences that as stress. Crying isn’t just noise, it’s how babies communicate discomfort, fear, or the need for closeness. When those cries go unanswered, the body releases cortisol, a stress hormone that helps us cope with threat. This is a normal response, but when crying continues without comfort, cortisol levels can rise sharply and stay elevated.
One small study by researcher Wendy Middlemiss looked at babies going through cry-it-out sleep training. What they found was striking: over several nights, babies cried less and appeared to settle, but their cortisol levels stayed high. At the same time, their mothers’ stress levels dropped once the crying stopped. In other words, on the outside things looked calmer, but inside the baby’s body, the stress response hadn’t fully switched off. Researchers described this as a mismatch between what the baby looked like and what they were experiencing physiologically.
Some researchers believe this quieting may reflect resignation rather than relaxation. In other words, the baby learns that crying doesn’t bring help, so the signalling stops even though the need for comfort remains. This doesn’t mean babies are being “harmed” in a dramatic or obvious way, but it does challenge the idea that silence always equals self-soothing or calm.
It’s also important to be clear and fair: not all studies find ongoing rises in cortisol after several days of sleep training, and short bursts of stress are part of normal life. But many experts emphasise that babies are still learning how to handle stress, and they do this through co-regulation, being soothed by a caregiver again and again. Responding to cries helps wire the brain systems involved in emotional regulation and safety.
So the question isn’t whether cry-it-out “ruins” babies as there’s no evidence that it does. It’s whether prolonged, uncomforted crying during a period of rapid brain development is something we want to normalise, especially when crying is a baby’s only way of asking for help. Sleep training may bring quieter nights more quickly, but should we be weighing that against the needs of a nervous system that is still learning what safety feels like?
For many parents, one of the hardest parts of cry-it-out isn’t the crying itself, it’s the instruction to ignore it. Crying is designed to be hard to listen to. It triggers a strong, almost visceral response in caregivers, particularly mothers, whose bodies are biologically tuned to respond to their baby’s distress. Hearing a baby cry activates stress and caregiving pathways in the brain, releases hormones like oxytocin, and creates a powerful urge to go to them. From this perspective, the discomfort parents feel during cry-it-out isn’t a sign they’re being weak or inconsistent, it’s a sign that their nervous system is doing exactly what it evolved to do.
Sleep training advice often reframes this instinct as something to overcome: parents are told that responding will “undo progress,” create dependence, or prevent babies from learning to self-soothe. Over time, repeatedly ignoring a baby’s cries can dull that instinctive response. Some parents describe feeling emotionally shut down, disconnected, or conflicted — torn between what they’re being told is “best practice” and what feels right in their bodies. While this emotional numbing is rarely discussed, it may have implications for how confidently and sensitively a parent responds to their child in the longer term.
Responsiveness matters because babies learn about the world, and about relationships, through patterns of response. When cries are consistently met with comfort, babies learn that their signals are effective and that their caregiver is reliable. This doesn’t mean responding perfectly every time, but it does mean that care is generally predictable and attuned. When parents are coached to ignore distress, even temporarily, it can interrupt that feedback loop, particularly if it goes against the parent’s own instincts or leaves them feeling distressed or disconnected.
None of this means that a parent who has used cry-it-out has harmed their child or broken their bond. Attachment is built over thousands of interactions, not a few difficult nights. But it does raise an important question: if a method requires parents to suppress their natural responsiveness in order to work, it’s worth asking what that costs, not just for babies, but for parents too.
For many parents, cry-it-out is not a philosophical choice, it’s a last resort. When you’re chronically exhausted, under pressure to return to work, and lacking meaningful support, survival takes priority. In a society that offers very little structural care for new families, sleep deprivation can feel unbearable and even dangerous. Preserving parental mental health matters deeply, and the long-term impact of a parent who is supported, functional, and emotionally available should never be underestimated. No one should ever feel judged or shamed for the choices they make in that place of desperation.
At the same time, it’s worth widening the conversation beyond individual decisions to the culture that shapes them. Broken sleep in babies and toddlers is developmentally normal, even though it’s incredibly hard to live with. Night waking isn’t necessarily a sign that something is wrong or that a baby needs fixing. Research consistently shows that infant sleep improves with age, whether or not sleep training is used, raising the question of whether we are too quick to pathologise a phase that most children grow out of naturally.
If cry-it-out doesn’t feel right, there are gentler ways to support sleep that don’t rely on ignoring distress:
