The Sleep Window!

What is a Cortisol Rush… and why does it matter for your baby’s sleep?

A cortisol rush is the body’s natural defence mechanism when it has run out of energy but still needs to keep going.

As adults, we’ve all felt it. You work all day, go out all night, and on the way home you think you’ll sleep for hours because you’re exhausted… BUT when you finally get home you feel wired and hyperactive. Then when you do fall asleep, your sleep is restless, you wake often, wake early and feel tired.

Babies are no different!

Our bodies can only stay awake for a certain amount of time. As sleep approaches, the body produces melatonin — the sleepy hormone — during what we call the sleep window.

If your baby isn’t asleep or settling by the end of that sleep window, the body releases cortisol (the stress hormone) to give them a burst of energy to keep going.

✨ That sudden burst of energy after tired signs?
That’s a cortisol rush.

And here’s the tricky part…

Once cortisol kicks in, it can be very hard for babies — especially those who can’t self-settle yet — to fall asleep. Keeping a baby awake for long stretches (5–6 hours or more) can make settling incredibly difficult and can even worsen early morning wake-ups.

Missing sleep windows can also contribute to those dreaded early starts to the day. The first sleep of the day plays a huge role in preventing cortisol build-up, which is why your baby’s first awake window should usually be the shortest.

The takeaway?

Learn your baby’s tired signs.
Understand their sleep windows.
Support enough daytime sleep — and the right bedtime.

Small adjustments here can make a big difference to your overall sleep journey

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