Sleep training and cortisol

Sleep training, cortisol & stressed out babies...?

I read an interesting article recently that was analysing different research on infant stress and cortisol levels, particularly in regards to "sleep training".

Now, I don't actually like the name "sleep training". The "training" part of it makes the term sound unnatural and regimented. For the sake of this article, I will call it sleep training though, because despite the different connotations and interpretations, sleep training generally just means a baby is learning the skill of falling asleep independently when they are developmentally ready to.

This can be achieved through many, many methods and there are countless arguments on either side of the sleep training fence - some are vehemently opposed to it and some aren't. A lot of the opposing views stem from a general misunderstanding about what sleep training actually means. By many, sleep training is viewed as being totally cry-based - as in a parent abandoning their child to cry alone until they give up and fall asleep. Words like "cry-it-out" or "extinction" or "Ferber" feature here, however, there are actually many different forms of baby sleep training and they don't have to involve crying. (See THIS article for more info).

What I want to focus on in this article though, is the broad claim that any form of sleep-training causes immense stress to a baby due to elevated cortisol levels, leading to emotional damage and long-term brain damage. In actual fact, a good friend of mine was told this recently by a health practitioner who I can only describe as being incredibly misinformed, judgemental, old-fashioned and just plain wrong.

So let's see what the research says, shall we?

In this article:

  • What is cortisol?
  • Is there a rise in cortisol levels when sleep training?
  • Is crying bad for my baby?

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What is cortisol?

Cortisol is often referred to as the "stress hormone". Despite it's (over-embellished) reputation as being extremely damaging for us, cortisol is a hormone that naturally features in our everyday lives and is released as part of our circadian rhythm. It isn't just related to profound stress.

What I find most interesting though is that studies have revealed the ways that babies respond to different forms of stress and it turns out that not all crying leads to a rise in cortisol levels. Also, not all cortisol elevations are necessarily bad or sustained.

A baby will experience a rise in cortisol when something new or unexpected happens, like a newborn baby having a bath, or having their diaper changed, or receiving an immunisation. This is why young babies will often cry when being put in the bath or while being changed. We're certainly not going to stop bathing or changing our babies because it elevates their cortisol levels are we?!

No. What ends up happening is that after a few days, babies will stop reacting to the bath with a stress/cortisol response. This isn't because they've "given up crying", it's simply because they have learnt from the experience and have moved through the stress response to a more positive response.

Cortisol is not always the enemy we think it is.

Is there a rise in cortisol levels when sleep training?

Studies have actually found that the levels of cortisol a baby releases during times of short term "stress" are actually lower (by 100-200%) than the cortisol levels babies naturally produce throughout the course of each day. Cortisol levels have also been found to be far higher in babies and children who are overtired, than those who experience some form of sleep training.

Furthermore, and this is super interesting, researchers have found that there is a more sustained and elevated cortisol response in a child starting daycare, than there is after a few days of "sleep training". And this is referring to very traditional cry-it-out sleep training techniques too (which we don't actually use in our Sleep Programs).

I'm sure we can all agree that starting daycare is not going to cause "permanent brain damage" or an "abandoned emotionally-crippled child" and yet, these are the phrases bandied around by sleep training scare-mongers.

Is crying bad for my baby?

No one likes hearing their baby cry, however, crying doesn't mean your baby is being damaged each time they do it. The human race simply would not have survived if each time a baby cried they were being emotionally or mentally injured! Luckily, our countenances are not that delicate.

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And by the time you have more than one child, you often have no choice but to let your baby cry at certain times. Imagine this scenario: your toddler is toilet training and needs to go to the toilet (with your help) but your baby is tired and has started crying. You cannot leave the toddler to wet herself so you can comfort the baby, when you know the baby is actually fine, just tired. Of course you help the toddler and the baby just has to wait.

These sorts of situations are commonplace when you have more than one child. And we can be assured that our babies are not suffering long-term brain damage simply from being the youngest child and crying more often than their older sibling had to!

So yes, during a period of changing a baby's sleep habits, there can be some crying, even with the gentlest methods. Of course your baby is going to protest any change to the status quo! They are not protesting because they're traumatised, just because they are tired and want to go to sleep, but now the situation for sleep is a bit different and unexpected.

My 6 year old still responds like this. Almost every Sunday we have pancakes for breakfast, but occasionally, we don't. She wakes each Sunday expecting pancakes and if I tell her we're not having them that day, she cries and cries. She is upset because it's not what she expected; it's different to the usual routine.

I can see how it must be quite confusing for her and I admit, it's unfair on my part, because it occurs so inconsistently. If I decided we weren't having pancakes ever again on a Sunday, she'd protest the change, without a doubt, for a couple of Sundays, but then no-pancakes would become the norm.

Protesting unexpected change is part of being human.

Your baby, in the context of a loving and responsive family environment, is not going to be placed under intense or irrevocable stress from a few days of guiding them towards new sleep habits. This holds true even if you are using a cry-based method (and everyone is free to choose what they think is best for their family without judgement).

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I can guarantee you your baby will continue to cry for their needs to be met at other times during the day. They will still cry when they're hungry, when they're upset, when they're tired, when they're hurt. They will, however, most likely stop crying when going to sleep and that is because they've moved through the experience to form a positive response. They've learnt a new skill and it's not different or dramatic or unexpected for them anymore; it's just sleep and sleep is not complicated.

Sleep training does not exclusively mean cry-it-out. Sleep training does not mean you are causing your baby brain damage or chronic stress. Working gradually towards better sleep is, in the short and long term, going to mean your baby has lower cortisol levels overall than a baby who continues to be overtired or sleep deprived. And you CAN teach your baby to fall asleep without leaving them to cry.


"Two days in and you guys have changed my life!!!! I've been battling anywhere between 4-6 wake ups a night for over a MONTH! One day on the Program and she went down without a hassle at 7 PM (when I would previously have to rock for an hour or two). Many, many thanks! I'm seeing so much promise here and my baby is actually happier and less fussy today. The best part? Little to NO crying for us! I'm so glad I gave this Program a try over traditional sleep training methods. Babe and I are so happy." - Jamie

If you're thinking about starting sleep training or would like to start guiding your baby towards self-settling, our comprehensive Sleep Programs contain several gentle methods to choose from, that are suited to your baby's age and current sleep associations.



Callahan, A. (2012). Helping Babies Cope With Stress and Learn to Sleep. The Science of Mom.

Shonkoff, J.P. and A.S. Garner. The lifelong effects of early childhood adversity and toxic stress. Pediatrics. 129(1): p. e232-46. 2012.

de Weerth, C., R.H. Zijl, and J.K. Buitelaar. Development of cortisol circadian rhythm in infancy. Early Hum Dev. 73(1-2): p. 39-52. 2003.

Gunnar, M.R. and B. Donzella. Social regulation of the cortisol levels in early human development. Psychoneuroendocrinology. 27(1-2): p. 199-220. 2002.

Middlemiss, W., D.A. Granger, W.A. Goldberg, and L. Nathans. Asynchrony of mother-infant hypothalamic-pituitary-adrenal axis activity following extinction of infant crying responses induced during the transition to sleep. Early Hum Dev. 88(4): p. 227-32. 2012.

Gunnar, M.R., N.M. Talge, and A. Herrera. Stressor paradigms in developmental studies: what does and does not work to produce mean increases in salivary cortisol. Psychoneuroendocrinology. 34(7): p. 953-67. 2009.

Ahnert, L., M.R. Gunnar, M.E. Lamb, and M. Barthel. Transition to child care: associations with infant-mother attachment, infant negative emotion, and cortisol elevations. Child Dev. 75(3): p. 639-50. 2004.

Vermeer, H.J. and M.H. van IJzendoorn. Children’s elevated cortisol levels at daycare: A review and meta-analysis. Early Childhood Research Quarterly. 21: p. 390-401. 2006

Scher, A., W.A. Hall, A. Zaidman-Zait, and J. Weinberg. Sleep quality, cortisol levels, and behavioral regulation in toddlers. Dev Psychobiol. 52(1): p. 44-53. 2010.

Karraker, K.H. and M. Young. Night Waking in 6-Month-Old Infants and Maternal Depressive Symptoms. J Appl Dev Psychol. 28(5-6): p. 493-498. 2007.

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