Does Sleep Training Cause Stress in Babies and Toddlers?

Can sleep training cause stress- and even elevated cortisol levels- for babies and toddlers?

A common question I get from parents is whether sleep training causes stress or elevated cortisol levels in babies and children. This is a great question, and one that makes perfect sense for loving and in tune parents to ask. After all, very few parents- if any- are okay with the thought of their children enduring a harmful stress situation. With so much misinformation on the internet about child sleep and sleep training, I want to answer the question fully, with an answer rooted firmly in evidence and the science of child development.

Where the claim comes from

A common study cited by those opposed to sleep training which claims to show the “ill effects” of sleep training is called the Middlemiss study from 2012.

The circumstances under which this study was conducted are as follows: 25 infants ages 4-10 months participated in what is called an “in-patient” sleep training intervention. The mothers of these infants took their children to the hospital, and at bedtime then handed the children to nurses and went out of sight. The nurses put the babies down and then left them with no soothing until they fell asleep. The nurses swabbed their cheeks before and after the babies fell asleep to measure their cortisol levels. The researchers took less than 72 hours of data from 25 infants being sleep trained in a hospital by strangers and asked, “Did they have a rise in cortisol?” The answer is yes! But this tells us absolutely zero about whether sleep training is problematic. 


Simply the limitations of the study. 

1. This study took only 48 hours of measurements

The first measurement occurred on night one, 24 hours later on night two, and 48 hours from the start on night three. Then they stopped taking data. 25 infants is also an extremely small sample size. It is very much NOT a high quality study. There were absolutely no follow ups.

2. This study did not include a control group

In addition, this study did not have anything else we’d expect from any study of meaning, including a control group. It was a very strange situation that was almost guaranteed to cause some level of stress in the babies, because they were in a new place, handed to strangers, being swabbed inside their mouths, going to bed in a place they’d never been, without their parents and without any soothing or check ins whatsoever.

A good quality study would have had control groups- babies in their own homes with their own parents soothing them, for example, which is what the vast majority of real-world sleep training looks like. The rise in cortisol could have been from any one of those strange factors but we don’t know because there were no control groups.

3. There were no baseline measurements of cortisol taken.

What I mean by this is that cortisol levels were not measured before the baby was taken into the sleep training situation. Babies who are simply tired can have elevated cortisol levels, so it’s hard to claim they were “high” when we don’t know what they were before being taken from their parents and starting the experiment.

4. The study was meant to induce stress, and was not meant to display harms of sleep training

Furthermore, this was never meant to be the “gotcha” on sleep training- it was meant to see if mothers and babies cortisol levels stayed the same through the intervention. The mothers’ cortisol levels went down on the third night when babies fell asleep faster without crying, but babies’ cortisol remained higher. This is right in line with what we’d imagine would happen less than 3 days into a strange situation for a baby, based on other studies we have that show after starting daycare, childrens’ cortisol levels remained higher for about two weeks. We would not expect them to be perfectly acclimated to a new situation within hours. On the other hand, for the mothers in the study, the babies not crying as much on the third night would be the equivalent of getting a daycare text saying “today is going great!” vs a text that their child is distressed. It would help them feel calmer. This makes sense.

There is no standard to which we hold parents and children to exhibit all the same hormonal levels at all times. As a matter of fact, it is an asset to the parent-child dyad if parents are able to stay regulated even when a child is upset. This can provide enhanced co-regulation.

So in conclusion, we leave this short, small, low-quality study knowing that babies had elevated cortisol levels in a strange hospital with strange people with no parents around doing something strange to them and think…. “Yes, and?”

Despite the study being improperly used, sleep training likely does cause a stress response!

Now you know that our basis for believing that cortisol rises during sleep training is this specific study. For the purposes of exploring this topic, let’s assume that cortisol does rise and babies do experience a level of stress during sleep training, especially if it’s their first time ever being laid down in their crib without, say, eating all the way to sleep first. I think it’s reasonable to assume that with a new situation that involves something novel or upsetting- including even baby’s first bath or exam- that there likely would be some sort of stress and therefore a cortisol rise.

But again, hypothesizing, this stress response would be generated in the way that a car ride with crying, doctors appointment, tongue tie revision, new caregiver and many other situations can cause stress for a child from day one of their little life.

Stress has a negative connotation, but it is not always harmful

I know that the word stress has a negative connotation (who likes to be stressed?) but did you know that stress is expected and necessary for development and can be a positive thing in many different contexts, including being the precursor to gaining literally any skill and building resilience? We all experience stress during change or learning anything new.  Such positive things as making new friends, practicing a sport, traveling to a new location and more induce a stress response in our body.

To understand if this is problematic, we have to understand the three types of stress identified in child development research, and their effects.

There are three kinds of stress- positive, tolerable, and toxic. We’ll be exploring the definitions, examples, and effects of each type of stress.

Positive stress

Positive stress refers to short-lived, mild-to-moderate stressful events in which a parent or caregiver assists to help a child get through the stressful event. 

Examples of positive stress events include starting daycare, shots, doctor visit, swim lessons, or meeting new people

Effects: elevated cortisol, increased heart rate, frustration or distress. Alleviated when brought back to baseline and reunited with or supported by attached caregiver.

Tolerable stress

Tolerable stress refers to a longer and more severely stressful event in which the child has a physiological and biochemical response that has the ability to cause lasting damage. “In tolerable stress responses, once the adversity is removed, the brain and organs recover fully given the condition that the child is protected with responsive relationships and strong social and emotional support.”

Examples of tolerable stress include death of a loved one, hospitalization, divorce, or a severe accident

Effects: the important thing to know is that tolerable stress has the potential to be harmful, but the buffering that occurs with the presence of support and an attached caregiver makes it tolerable and causes no long-term ill effects.

Toxic stress

Toxic stress refers to extreme, prolonged, frequent stress without attachment or the accessibility of a loving caregiver to help the body return to a baseline after the stress response.

Examples of toxic stress include chronic starvation, verbal and physical abuse, untreated chronic parental depression, violence. No secure attachment figure in life to support through the trauma. 

Effects: brain damage, addiction, psychosis, PTSD, attachment disorders

I’ll leave it to you to decide if learning to fall asleep in their crib, supported by their loving caregiver, belongs in the “doctors appointment with shots” category- possibly unpleasant but not harmful- or the death, starvation and chronic physical abuse category with no attachment figure in their life category. The answer is very plain to me, but I don’t think it’s just a biased hunch. 

There have been zero long term effects, as seen in children who have suffered toxic stress, have ever been identified in any study pertaining to sleep training.

If there was toxic stress occurring during sleep training, children who have been sleep trained would have actual structural brain differences on top of attachment disorders and emotional differences that we would easily be able to observe and measured. And they do not.

Children who have been sleep trained have no attachment or physical or mental health differences than those who have not gone through any sleep interventions, as evidenced by dozens of studies including this one (which included hundreds of children and a FIVE year follow up), this one, and this one (which actually suggests secure attachment behaviors increased during the day following sleep training- which makes sense knowing what we know about chronic sleep deprivation and how it can affect families interactions and mental health).

Is Shutdown Syndrome Real?

Anti-sleep training advocates have run absolutely wild with the Middlemiss study, even coining a term for the state in which a baby no longer cries very much when exposed to a situation but still has elevated cortisol levels, referencing the one measure taken 48 hours into the Middlemiss experiment. This term is apparently, “Shutdown Syndrome.”

In all my years of hunting for evidence-based sleep research, I’ve never been able to find a credible source for the term “Shutdown Syndrome.” It is not accepted as a medical diagnosis or condition, and seems to have its roots as a term coined by Dr. Sears, the father of Attachment Parenting. He describes it in blogs as “a sort of baby depression.” He attributes this condition to babies of supposed clients who have sleep trained.

This term has been taken a repeated by… well, mom blogs and several “anti sleep training” big names. Again, without scientific basis and without acknowledging that this term is not actually a real condition.

This is one of those difficult claims to refute because basically the refutation is… there is no evidence to support this claim. People use dramatic and emotionally manipulative claims like “shutdown syndrome” is what happens to a baby when they cry and do not receive a response. They don’t stop crying because they become more comfortable, or become tired. They shut down to a “deathlike state” to “preserve their energy.” Again… this is just… to use equally scientific terms… utter baloney.

We have seen children completely stop signaling- day or night- in extreme chronic toxic stress situations like Romanian orphanages where children had no parents, no one ever touched them and they were confined to cribs for years, fed by thickened bottles tied to their cribs even as toddlers, and abused. But that is such an offensive comparison to a baby falling asleep in their crib at bedtime attended by loving, attached caregivers who meet their needs day and night, that it’s literally not even worth mentioning.

From everything we know about child development, the reason a child exposed to a positive stress event eventually stops being upset by the event is that they have become more acclimated to it as the novelty wears off. Even if cortisol levels remain higher for a temporary period of time, as we see with new daycare exposure, this does not mean a child has shut down. It means that they are moving through the positive stress response and becoming more comfortable, even while it’s still very new.

Sleep Training is a Positive Stress Event, and a Valid Choice

So there you have it- sleep training can be a positive stress event for children, just like many daily activities that children experience. As always, sleep training is an intervention and a choice, not a necessity! No family should feel pressured to sleep train if what you are doing is working for you or if it feels like the best choice for you and your family. However, if you know it is the right choice for your family and do choose to sleep train, you can rest easy knowing that by all evidence we have, it is perfectly safe for your little one and that they can handle the transition perfectly well with your love and support.

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I’m Katelyn,
Award-winning pediatric sleep consultant, child development expert, and most importantly, wife and mom.
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