Baby Sleep Biology


Baby Sleep Biology

I’m so excited to introduce Kerry Secker, who is  is a paediatric sleep consultant and the founder of her unique Care It Out sleep approach. She’s on a mission to share sleep education that you don’t HAVE to sleep train and you CAN improve your family’s sleep with an approach that’s sensible, scientific AND caring.

A little bit about Kerry

Kerry’s approach to sleep is that all families and children are unique and there isn’t a quick fix or one size fits all solution when it comes to children’s sleep; her mantra is one size sucks!  She’s also passionate about having realistic sleep expectations and that sleep doesn’t need fixing; issues are only an issue if they are one for your family!

Kerry, a former Nanny, has over 18 years’ experience supporting and advising families with sleep, often writes for the Huffington Post and runs her popular caring sleep sessions across the UK.

If you are a sleep seeker, experiencing the bed dread or have a night time sleep stealer Kerry can support you to improve your child’s sleep the caring way. There is always a biological reason and sleep science behind bedtime behaviour and always a caring way forward. 



Instagram: @careitoutsleepconsultant


It’s All About Bedtime Biology Baby!

By Kerry Secker 


When it comes to a settled night’s sleep for your small there’re two important hormones:

Melatonin: This is the sleep hormone controlled by the circadian rhythm or sleep system which is fully developed between the ages of 5-6 months.

Short frequent naps and inconsistent nights are natural until your baby is around 6 months when their sleep system is fully established

Cortisol: AKA baby red bull: This is the opposite of melatonin and it’s designed to keep your small in a high state of alert and awake.

The magic of melatonin

At around 6 months old your small’s sleep system is up and running meaning they produce melatonin on a 12 hour sleep shift:

3pm: Melatonin starts to slowly rise and they begin to slow down in preparation for sleep

7pm -7.30pm: Their melatonin is at its peak

When it’s at its peak the level stays consistent until midnight

Midnight: Melatonin slowly starts to leave their body

3am: All their melatonin has left the body

Sleep Stages

Bedtime to midnight: melatonin levels should be fairly high and it’s the deepest sleep stage. It’s usually a good block of sleep and if your baby wakes they’re usually easily settled.

Midnight to 3am: Your baby can wake more frequently andyou may need to do a bit more work to get them back to sleep. It’s not uncommon that some babies may even be wake for long chunks of time!

3am to midnight: By now all the melatonin has left their body and sleep is at its Lightest. Your small may appear restless, unsettled and more. Again some babies may be awake for long periods or even wake up for the day now!

Cortisol Clues

When you little one is overtired you would think they would just get so tired and just fall asleep; nope!

Even though we all want more sleep it’s actually a rather pastime because our body totally shuts down and is unaware of what’s going; potentially putting us in danger!

When your small is overtired your small doesn’t know they’resafe to sleep so they produce cortisol to keep them in a heightened state of alert and awake!

Once your little one produces cortisol they can take 6 times longer to settle to sleep

Cortisol clues

These are the signs your small may be over tired:

🔎They wake up early in the morning 🔎They fight and resist their naps 🔎They take short naps of 30 minutes or less 🔎They are fussy, clingy and tearful especially towards the end of the day 🔎They’re totally wrecked at bath time 🔎They’re begging for bed after their bath; crying, upset and unsettled 🔎They crash out as soon at their bedtime feed. They may be too tired to feed properly and/or leave a lot of their milk 🔎They get the sleep sillies; they are manic, overwired but don't look tired 🔎 They resist going to sleep and/or bedtime takes an age to settle them 🔎 They wake 30-40 minutes after going to sleep 🔎 They wake frequently during the night 🔎 They wake up frequently post-midnight 🔎They’re awake for long periods post-midnight


The sleep see saw

Balancing these two hormones is the first step to getting a settle night’s sleep. Control the cortisol and match their melatonin and you’re over half way to a settled night’s sleep.

Sleep steps for balancing melatonin V Cortisol

Naps control the cortisol

These are the first step to a settle night sleep because they prevent over tiredness sand control the cortisol.

This is a rough guide to naps by age: 


Nap Needs per day

6 months and younger

3-4 hours’ sleep over 3 to 4 naps

6 to 9 months

2-3 hours’ sleep over 2-3 naps

9 to 18 months

2-3 hours’ sleep over 1-2 naps

18 months to 3 years

1-2 hours nap over 1 sleep

3 to 5 years

Sometimes 1 nap (most lose between 3 & 5)


 Best bedtime

Pushing bedtime too late can quickly undo all your good work of controlling the cortisol during the day and ideally your small is settled to sleep when their melatonin is at its peak.

Best bedtimes by age:

Under 6 months          

Keep to their nap gap. So if they go 2 hours between naps during the day bedtime no more than 2 hours from their last nap of the day

6 months to 18 months      

Ideally no more than 4 hours from 3pm

Over  18 months                

Bedtime can be pushed to suit your little one but I would generally suggest between 4-5 hours from 3pm


If your small is battling bedtime try bringing their bedtimeearlier; Just 10 -15 minutes can make such a positive difference to how they settle to sleep, their night sleep and the time they wake up.

Support at night

Meeting your smalls emotional needs at night is never spoiling them or creating bad habits but try to be mindful of what they’re communicating to you. If they aren’t asking for support try to give them the sleep space they’re asking for.

 Post-midnight movement

After midnight melatonin levels are decreasing and sleep is getting lighter

It’s natural that your little one may look awake, unsettled or restless but this is all perfectly natural and it doesn’t always mean they need support from you.