The paradox of infant overtiredness confounds many parents: a baby who needs to sleep badly becomes harder to settle, not easier. Understanding why this happens, and how to recognise early tired signs before the overtiredness threshold is crossed, is one of the most practically useful aspects of infant sleep management.
Healthbooq helps families read their infant's sleep cues and respond at the right moment.
The Cortisol Mechanism
When an infant (or any human) has been awake beyond their optimal wake window, the body produces cortisol as a compensatory stress response. Cortisol is a stimulant — it is the same hormone involved in the "fight or flight" response. In the context of overtiredness, cortisol production has the effect of:
- Increasing arousal and apparent energy
- Making it harder to transition to sleep
- Producing more fragmented sleep once the infant eventually falls asleep
- Driving earlier morning waking
This explains the "second wind" phenomenon: an overtired infant who seemed about to collapse suddenly revives and appears more energetic and harder to settle.
Early Tired Signs (the Optimal Window)
These signs typically appear as the infant approaches the end of their optimal wake window, before the cortisol response:
- Eye rubbing — one of the clearest and earliest cues in many infants
- Ear pulling — though note that ear pulling can also indicate teething or ear discomfort in older infants
- Decreased visual engagement — the infant who was attentively watching faces or objects becomes less responsive
- Slowing of movement — less kicking, less arm movement
- Yawning — reliable in some infants; less reliable in others
- Glazed or unfocused gaze
- Sucking on hand or fingers
Late Tired Signs (Approaching Overtiredness)
These signs indicate the optimal window has been missed:
- Increased crying and irritability
- Arching the back
- Clenching fists
- Difficulty being comforted by the usual means
- The "second wind" — a sudden apparent energy revival
The Practical Application
The goal is to begin the settling process when the early signs appear — not waiting for the late signs, by which point the cortisol response may already be triggered. For new parents, this requires observation of the individual infant's specific cue sequence, which varies between babies.
Key Takeaways
Overtiredness in infants is not simply being very tired — it is a physiological state in which accumulated fatigue triggers a cortisol stress response, making it harder, not easier, to fall asleep. The classic paradox of overtiredness is that the child appears wired or more active at the very moment they most need to sleep. Recognising the early signs of tiredness — before the overtiredness threshold — is the key to catching the optimal sleep window.
