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Among the hot-button topics I hear a lot about (food dyes, vaccines), sleep training a baby is one of the most contentious. By “sleep training,” people typically mean some form of “crying it out” — broadly, any system where you leave the baby in their crib on their own at the start of the night and sometimes let them fall back to sleep on their own if they wake up during the night. The description refers to the fact that if you do this, your baby will cry at some points, especially early on in the process.
There are various versions of this (Ferber, Weissbluth, etc.), and they all take slightly different approaches (whether you check on the baby, how long you wait before going in, whether you stay in the room). Sleep training is popular with parents and advocated by many pediatricians. Yet go on the internet, and you’ll immediately find random people detailing the extensive long-term damage sleep training will do to your child. They’ll also tell you it doesn’t work.
What does the data actually say about sleep training? Does it work and, more importantly, is it dangerous?
Does sleep training work?
Yes, sleep training works for improving sleep. It’s generally recommended that you start at around 4 to 6 months because babies can better self-soothe at that age. However, you may be able to do it even earlier.
There are many, many studies that show this. A 2006 review covered 19 studies of the unfortunately named “Extinction” method — the form of “cry it out” in which you leave and do not return — of which 17 showed improvements in sleep. Another 14 studies used “Graduated Extinction” — where you come in to check on the baby at increasingly lengthy intervals — and all showed improvements. A smaller number of studies covered “Extinction with Parental Presence” — in which you stay in the room but let the child cry — and these also showed positive effects, which is defined as a reduction in bedtime problems and/or night wakings.
These effects persist through six months or a year. This means that children who are sleep trained are sleeping better (on average) even a year after the training.
These methods do not completely solve all sleep problems from day one. And some children respond better than others, as do some parents. Not every baby who is sleep trained will sleep through the night every night, but they do sleep better on average.
However, there is simply a tremendous amount of evidence suggesting that sleep training that includes “cry it out” is an effective method of improving sleep.
It is worth noting that most of these studies — and, indeed, virtually all sleep books — recommend a “bedtime routine” as part of any sleep intervention. There isn’t much direct evidence on this — the review refers to it as a “common sense recommendation” — but it is generally included with all intervention approaches. The idea is to have some activities that signal to the baby that it is bedtime: putting on the baby’s pajamas, reading them a book, singing a song, and turning off the lights. Basically, no one recommends putting a fully clothed baby in the crib with the lights on, telling them it is bedtime, and closing the door.
What are the benefits of sleep training?
Sleep training improves the amount of infant sleep. Settling into a good sleep routine — one that will ensure longer and higher-quality sleep — could have long-term positive effects for children.
There are also benefits of sleep training for parents. These interventions seem to be very successful at reducing maternal depression. To take one example, an Australian study of 328 children randomized half into a sleep-training regime and the other half into a control group. Two and four months later, the authors found that the mothers of babies in the sleep-training arm were less likely to be depressed and more likely to have better physical health. They were also less likely to use health services.
A 2023 meta-analysis found significant impacts in improving total infant sleep and reducing maternal depression. In some cases, the effects are very large. One small (non-randomized) study reported that 70% of mothers fit the criteria for clinical depression at study enrollment and only 10% after the intervention.
Sleep training isn’t a panacea, and it works better for some babies than others, but there do seem to be overall benefits.
Where do the concerns with “cry it out” originate?
At its core, the concern from the opponents of “cry it out” is that your baby will feel abandoned and, as a result, struggle to form attachments to you, and ultimately to anyone else. It is worth a brief digression on where this idea comes from.
The answer: Romanian orphanages.
In the 1980s, a deep failure of reproductive policy left thousands of infants and children in Romanian orphanages. These children suffered all kinds of tragic deprivations, including limited food as well as physical and sexual abuse. In addition, they had almost no adult contact as infants and children. They were left in their cribs for years with virtually no human contact, resulting in very late physical development, along with mental and psychological costs. Researchers who visited them found that the children could not form bonds with others, and many of them have struggled their whole lives.
This influenced the attachment-parenting philosophy, including views on the use of “cry it out.” One of the things visitors noticed in these places was the eerie quiet of the rooms the children were kept in. Infants and babies didn’t cry because they knew no one would come. The argument is that “cry it out” is the same thing: Your baby will stop crying because they know you will not come, just as the children in these orphanages did. And just as in those settings, their ability to attach to you and others will be forever changed.
The experiences of the babies and children in the Romanian orphanages were terrible and shameful and should never have happened. But it is also not comparable to the experience of most infants whose parents use “cry it out” methods. These methods do not leave infants unattended for days without human contact, nor do they involve other forms of physical and emotional abuse.
Obviously, “cry it out” critics understand this, but they may see this as a continuum. The children left in these orphanages suffered extreme long-term consequences. Children who experience other types of chronic life stress — physical abuse, serious neglect — often have long-term problems. A few nights of sleep training probably will not do that, but who knows whether they endure smaller damages?
Fortunately, the literature does know, at least to some extent.
Does “cry it out” harm infant attachment?
There are a number of good randomized trials that conclude that the “cry it out” method of sleep training is not harmful to your child. One representative study, from Sweden, published in 2004, took 95 families and randomized them into a sleep-training regime involving a form of “cry it out.” The authors focused on whether behavior during the day was impacted by the nighttime; basically, they asked whether the infants were less attached to their parents during the day as a result of being left to cry during the night.
This particular study found that, in fact, infant security and attachment seemed to increase after the “cry it out” intervention. It also found improvements in daytime behavior and eating, as reported by the babies’ parents. Note that this is the opposite of the concerns raised about “cry it out” methods.
This study is not alone. A 2006 review of sleep-training studies, which included 13 different interventions, noted the following: “Infants who participated in sleep interventions were found to be more secure, predictable, less irritable, and to cry and fuss less following treatment.”
This evidence focuses on immediate impacts on the infant. But that isn’t necessarily the main concern among those who shun “cry it out.” Instead, the worry is about longer-term impacts. Yes, the infant cries less, maybe even less during the day — but, critics believe, it is because they have given up, not because they are happier.
To more fully address this, we need to follow sleep-trained children to older ages to see whether there are long-term risks. This adds to the difficulty of running a randomized trial, of course, since longer-term follow-up is both difficult and expensive. However, we do have one example.
In the study run in Australia that I mentioned above, with 328 families recruited when their babies were eight months old, the authors first showed that the intervention improved sleep and lowered parental depression. But they didn’t stop there. They returned to evaluate the children a year later and, most notably, five years later, when the children were almost 6. In this later follow-up, which included a subset of the original families, the researchers found no difference in any outcomes, including emotional stability and conduct behavior, stress, parent-child closeness, conflict, parent-child attachment, or attachment in general. Basically, the kids who were sleep trained looked exactly like those who were not.
There is also community-based data, which is less valuable than randomized data, but points in the same direction. An example is a 2020 study that surveyed parents about their sleep behaviors and then, later, evaluated maternal-infant attachment. They did not find any differences.
The data overall does not point to short or long-term issues for children with attachment as a result of sleep training.
Why am I hearing about concerns?
A number of academic articles argue against “cry it out” from a theoretical perspective. One good example comes from an article published in 2011 in a journal called Sleep Medicine Reviews. The authors of this article presented a case against “cry it out” largely based on the idea that infant crying is intended as a signal of distress, and parents should therefore not be encouraged to ignore it. They draw on attachment theories (i.e., the orphanage literature) and argue that parents who engage in this are ignoring their children’s efforts to begin communication with them.
The fact that “cry it out” works is not compelling to these researchers and, indeed, is an indication of harm. The primary argument offered by this and similar papers is that infant crying is a signal of stress (which is probably true) and that stress, even over a short period of days or weeks, may have long-term consequences for babies (which is speculative).
People in this space often point to one particular study to support these stress claims. That study, published in 2012, followed 25 infants and their mothers in New Zealand over a five-day inpatient treatment in a sleep lab. The goal of the stay in the lab was to sleep train the infants. Nurses in the study collected data on the stress hormone cortisol in both the babies and their mothers and were also responsible for putting the infants to sleep and monitoring the sleep training.
Before the sleep training each day, the babies’ and mothers’ cortisol levels were tested and recorded. This was done again after the infant fell asleep. On the first day, the babies all cried. Their cortisol levels were the same before the training and after they fell asleep. Their mothers’ cortisol levels were also the same before the babies cried and after they were asleep. This was the same on the second day.
On the third day, none of the infants cried (see above: sleep training works). However, they showed the same cortisol patterns: equal before bedtime and after they fell asleep. But for the moms, this changed: they had lower cortisol levels in the later period, when the babies weren’t crying.
The authors suggested that this presents a problem with sleep training. In particular, they note that after sleep training, the mother’s stress levels do not stay in sync with the infant’s, which they interpret as possible evidence that the attachment between mother and infant is weakening.
As others have noted, this is an overinterpretation of the study results. For one thing, there is no baseline level of cortisol given, so we actually have no way to know if the babies were even experiencing elevated stress. For another, the study stopped after three days (or at least the data reporting did), so we don’t know what happened later.
But even beyond this, it is unclear why differing levels of cortisol for moms and infants after sleep training is a problem. Effectively, this study shows that mothers are more relaxed after sleep training occurs, and that there are no other changes beyond raised cortisol levels for the infant. This seems like a positive result, not a negative one.
With a theoretical argument like this, it is nearly impossible to generate a full counterargument. They could argue that perhaps for some children, sleep training is devastating, and you do not know which ones. Or, maybe the harms only show up decades later when children reach middle age, and we haven’t followed them long enough. No study or evidence will rule this out. Of course, the converse is also true: maybe not sleep training is harmful, and you’ll only find out later.
For parents, having to make decisions now, we have to decide with the imperfect data we have. Which, in this case, does not suggest cause for concern if cry-it-out sleep training is what you choose.
How can I decide if sleep training is right for me?
This is the right question to ask. We are too quick to ask the wrong question: Is sleep training going to ruin my child? Or, do I have to sleep train? The answer to both of these is no. Cry-it-out sleep training should be in the toolbox, but it isn’t the tool you will necessarily pull out.
One important consideration: Parents who are less comfortable with the idea of sleep training find it harder, and it’s less successful. Basically, sleep training is a better fit for you if you are confident that it’s the right choice.
How can you decide? Here’s a quick road map.
Start thinking about this early: A common time to start sleep training is around 4 months. At this age, you’re probably not looking for your baby to sleep through the night, but instead, for them to fall asleep independently at the start of the night. It’s useful, if possible, to give yourself time to plan before you start (even if you decide to start later or not at all).
Plan for the long term: Think about what you want in the medium to long term. Are you planning for your child to sleep independently in their own room, or are you planning to co-sleep? (In the latter case, sleep training is less relevant.) This is worth discussing with your partner, if you have one, to get on the same page.
Think about your wake tolerance: Assuming you are planning to have your child sleep independently, the choice to sleep train will (on average) reduce the number of wake-ups. This is more important for some people than others. Based on other aspects of your life — your need for sleep, what you’re doing during the day, your other children, etc. — be realistic about what you can accommodate. There are people for whom getting up every couple of hours to soothe their baby, or sleeping in the room with the child to make this easier, is no problem. And there are others for whom that is not feasible. Neither of these is right or wrong; people are just different. A big reason to sleep train is to improve parental sleep, so the need for that should be part of the decision.
Make a plan: If you do decide to sleep train, make a plan that works for you and that you can stick to. You’ll find more details on methods here, and I recommend Healthy Sleep Habits, Happy Child if you’re looking for a longer book on this.
Ultimately, every family is different, and you may really not want to let your baby “cry it out.” You need to make your own choices, just as with everything else. But if you do want to sleep train, you should not feel shame or discomfort about that decision. The data, imperfect as it is, is on your side.
The bottom line
- Sleep training has been shown to increase an infant’s sleep quality and duration, aiding in development and teaching babies to self-soothe when waking overnight. It also significantly benefits parental mental health, reducing maternal depression and lowering overall stress.
- There is no evidence of short-term or long-term harm to children who have been sleep trained.
- “Cry it out” critics argue that ignoring an infant’s cries, even briefly, may negatively affect their ability to form attachments; this critique originates from Romanian orphanages in the 1980s that abandoned babies for months in cribs. However, standard “cry it out” techniques differ significantly from child abandonment.
- Some theoretical objections argue that crying signals distress and that ignoring it could adversely impact infant attachment and stress responses, but existing evidence supporting these claims is limited.
- Ultimately, whether you sleep train is a personal choice. There is no right or wrong answer here, but if you do want to sleep train, you should not feel shame or discomfort about that decision.
