One of the main concerns that parents have when they first start considering sleep training is whether they will harm the child in any significant way if they allow her to cry for some set length of time.

There's a reason why the answer to this question is not common knowledge already. Believe me, if extended crying had a straightforward connection to any serious harm to children, you'd know about it already. This is why I hate giving newspaper and radio interviews sometimes. And it's why this post has taken almost a week to write. Most people want a one-liner. They want the bottom line: Is it good or is it bad to let your baby cry when you're sleep-training? OF COURSE you want the bottom line. You want to do right by your baby. But the one-liner just doesn't exist. ANYBODY that tells you that the research is straightforward, that science has come up with a real answer, is simply not telling the truth. Intentionally or not, WAY too many sleep experts — from the "Attachment Parenting" camp to the hard-core CIO fans — profess that science has come up with the answer as to whether crying harms children in the long run. It's simply not true.

Having read far too many of the original studies that are related to the topic, here's my take. My best answer as to whether it harms a child when we let her cry for a while when sleep training is: It depends, but it probably doesn't damage children in any significant way (long-term outcomes, self-esteem, bond with parents, etc.). It depends because some kids are particularly sensitive to separations; it depends because parents can get so resentful of failed attempts at sleep training that they treat the child poorly and that, in turn, has detrimental effects (and we can't tease apart these effects from the amount of crying the child is doing); it depends because some children's crying, even the most minimal amounts, sends some vulnerable women into a tailspin of postpartum depression and we know that's not good for kids in the long run; it depends because some children become physiologically so aroused when they cry that they vomit or hyperventilate and, well, that's not good for some kids either; it depends because some children cry MORE when they're being rocked to sleep by well-intentioned parents than they would if they were left alone and ignoring that need that some kids have to be left alone (which they can't articulate) may actually be equally detrimental to some kids; it depends because many couples go through significant marital conflict when it comes to deciding how long to let their baby cry and marital conflict has repeatedly and consistently been found to have long-term negative consequences for children. So… how would you tease out whether it was the length of crying during sleep training or the marital conflict about the crying that made the biggest dent in a child's developmental outcomes? (You COULD do it, but the study would be very complex and it hasn't been conducted yet). So, yeah, it depends (and I could go on for much longer about all the factors that make this seemingly simple question so very, very complex).

But… however complex the issue may be, there are indeed studies that have been conducted to tackle the issue from various angles. Let me point you to some that have brought me around to my general conclusion:

In the review article in the journal Sleep that I keep referring to, they went through the best studies out there (a total of 52) and concluded that there were no appreciable differences in the effectiveness of the top 5 sleep training methods assessed (from CIO methods, to Ferberizing, to more gentle methods like "positive routines" or faded bedtimes). Then they looked for "collatoral damage" if you will. Here's the quote from the article directly: "A total of 13 studies selected for this review reported results pertaining to child daytime functioning such as crying, irritability, detachment, self esteem, or emotional wellbeing… Adverse secondary effects as the result of participating in behaviorally
based sleep programs were not identified in any of the studies [Did you catch that? NONE of the studies showed negative effects, even the CIO ones]. On the contrary, infants who participated in sleep interventions were found to be more secure, predictable, less irritable,and to cry and fuss less following treatment.Mothers indicated that behaviorally-based sleep interventions had no effect
on maintaining the practice of breast feeding or on infant’s total daily fluid intake."  If you go to the original paper I have linked, they cite all the studies that brought them to this conclusion — they're well-designed, published in reputable journals, reviewed by a committee of scientific peers.

Then there's a group of studies that don't directly address the question, but they're related in important ways.  Researchers have long been interested in whether crying itself is a bad thing for kids. Several groups of researchers have studied colic and its long-term impact on children. Most of them have come up with the conclusion that early, "excessive" crying (often referred to as colic) does not lead to poor outcomes for children (unless there are ADDITIONAL problems in the family like depression, marital conflict, poverty and so on). It may be that when crying PERSISTS over a longer period of time (rather than being temporary, which is the case for any sleep-training process) that negative outcomes become associated with crying. Here is one of many review articles that summarizes the findings.

Other researchers have been focusing more on the stress hormones released during crying fits and how those may impact on the long-term development of children. Crying is a physiological response to stress and it involves increases in blood pressure, heart rate, and cortisol levels (indicators of stress). A fantastic recent review article — by Megan Gunner, one of the most well-regarded neurobiologists in the field — goes through decades of research on stress levels and their neurobiological effects on children's long-term development. She, like many of her colleagues, conclude that PROLONGED high levels of stress (that are often, but not always, accompanied by lots of crying) leads to loads of poor outcomes for children. But again, this is PROLONGED stress — over months and years often — NOT crying that happens over a week or two and that lasts for short periods, relatively speaking (even an hour is a short period in this line of research). Just to give you an idea about the level of prolonged stress we'
re talking about here, these researchers study children from abusive and neglectful families (physically and emotionally), children who have recently been adopted out of institutions known to have neglected babies and children for years at a time (like the Romanian orphanages of the pre-Revolution era), and so on. Yes, stress can have a negative impact on children. Yes, of course, our jobs as parents is to try to minimize the amount of stress children go through. But the serious negative long-term outcomes associated with chronic elevated levels of cortisol are WORLDS away from even the most die-hard forms of CIO. And this is where I get on my soapbox: People who call themselves experts who cite this body of work as rationale for never allowing your child to cry (alone or in your presence) for some prescribed duration of time during sleep-training are seriously misrepresenting this body of research.

 One last point that I tried to emphasize in the book: We all want to have the most stress-free sleep-training experience for both our children and ourselves. EVERYONE wants to minimize their child's distress during sleep-training. The problem with picking the "right" sleep-training method for your child — the method that will provide the best results in the shortest period of "training" possible, with THE LEAST AMOUNT OF CRYING — is that, depending on the child, the most gentle sleep methods can have some kids wailing for hours out of frustration and the most hard-core CIO can have other children sleeping in 5 min. I have heard MANY stories from mothers who have used "no-cry" sleep solutions and been frustrated to high-hell with them because their child interprets these gentle methods as a big "tease." These children cry MORE when their mother is present, in the room, but shushing them and inching little by little away from them. They can cry for hours and hours in this type of frustrating experience. For other mothers, these same methods resulted in their babies sleeping through the night through a painless, cry-less transition. Just as many mothers SWEAR by "graduated extinction" or Ferberizing, claiming that before they Ferberized, their babies would cry in their arms for hours during rocking and bouncing sessions; during sleep-training, they cried LESS. And of course there are plenty of parents that have tried CIO methods and been traumatized by the amount of incessant crying their babies endured.

Crying in and of itself will not damage your child for good. There have to be other factors working to do that kind of damage. Yes, some children may show signs of insecurity the next day. Other children will show the exact opposite, seeming more jolly than they had PRIOR to sleep-training. If you feel that the method you're using is adversely effecting your child, then stop. Recharge for a few days. Try something else. Try again in the next optimal developmental window.

And as one who has ALMOST come through the other end of worrying about serious sleep concerns with my children, I have to say that I now have SO MANY more opportunities to screw up my kids. Sleep-training now seems like a drop in the "am I messing up my kids for good" bucket. Now I can yell at them for throwing food and worry about scarring them for life, I can be an irritable, tired, inaccessible mother when I get home from work and recall all that research on "the distracted mother", I can feed them things I don't know I shouldn't be feeding them because I don't do enough research, I can put chemical-ly sunblock and bug spray that will MESS WITH THEIR BRAINS FOREVER!

Ah… the joys of motherhood for all of us guilt-prone parents out there…