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Sleeping

The startle (Moro) reflex, explained

Article By
Anna
Published On
14 Jan, 2026
Read Time
6 minutes
  • The Moro or 'startle' reflex is an involuntary response where newborns suddenly fling their arms out, arch their back, and cry when they sense they're falling or hear a loud noise, functioning as a primitive survival mechanism. 
  • Startle reflex naturally fades between 3 to 6 months of age as your bub's nervous system develops and their movements become more deliberate and controlled. 
  • Swaddling helps manage startle reflex by securing baby's arms close to their body, creating womb-like comfort and stopping their own movements from disrupting sleep. 
  • You can reduce startling by handling baby gently and slowly, keeping the environment calm and quiet, using white noise to buffer sudden sounds, and sticking to predictable routines. 

Has your newborn ever suddenly flung their arms out wide, arched their back, and let out a surprised cry? If so, you've seen their startle reflex in action. 

While it might give you a fright the first few times you notice it, this automatic response is completely normal and actually shows that your baby's neurological development is right on track. 

Let's dive into what the Moro reflex is all about, what sets it off, and how you can help your baby feel more settled when it happens. 

What is a startle (Moro) reflex? 

The startle reflex (also called the Moro reflex) is an automatic response that newborns have when they sense they're falling or are startled by a sudden loud noise or movement. 

It's named after Austrian paediatrician Ernst Moro and is one of several primitive reflexes that babies are born with. 

When your baby's Moro reflex is triggered, you might see them: 

  • Fling their arms out to the sides with palms facing up and thumbs bent 
  • Arch their back and straighten their legs 
  • Cry out or look distressed 
  • Draw their arms back towards their body in a hugging motion 

The whole sequence only takes a second or two, but it's often enough to wake a sleeping baby or leave them feeling unsettled. 

This reflex is a key evolutionary survival response, designed to help infants grab onto their caregivers when they sense danger or feel unstable. 

What causes Moro reflex?

The startle reflex can be set off by different things in your baby's surroundings. Knowing what these triggers are can help you reduce unnecessary wake-ups, particularly during sleep times. 

Common triggers include: 

  • Quick movements: Laying your bub down too rapidly, or any sudden change in position, can activate the reflex. This is why babies often startle when you're settling them into their cot or bassinet. 
  • Unexpected noises: Sounds like a door banging, a dog barking, or even someone sneezing can set off the response. 
  • Feeling unsupported: When babies get that falling sensation or feel like they're losing physical support, the reflex kicks in automatically. 
  • Sudden brightness: An abrupt change in lighting, like switching on a bright light in a dark room, may startle your baby. 
  • Their own movements: Sometimes babies can startle themselves during sleep as they move between sleep cycles, or from their own jerky movements. 

The Moro reflex is entirely involuntary; your baby can't control it at all. It will naturally fade as their brain and nervous system continue to develop. 

When does startle reflex go away? 

As your baby's nervous system matures, their movements become more intentional and coordinated, and primitive reflexes like the Moro reflex gradually disappear. Most babies will naturally grow out of the Moro reflex somewhere between 3 to 6 months of age. 

How long do newborns have startle reflex? 

The startle reflex is there from birth and usually starts to lessen around the 3-month mark. By 5 to 6 months, most babies will have completely lost this reflex. If your baby’s Moro reflex is still going strong beyond 6 months, it's worth having a chat with your GP or child health nurse. 

How can you help startle (Moro) reflex? 

While you can't stop the Moro reflex completely (it's a natural and healthy response), there are plenty of gentle techniques you can use to minimise startling and help your baby feel more secure: 

  • Keep things calm: Maintain lower noise levels, especially during naps and bedtime. White noise machines can help mask sudden sounds that might trigger the reflex. 
  • Handle with care: When picking up or putting down your baby, keep your movements smooth and unhurried. Make sure you're supporting their head and body properly during transitions. 
  • Be gentle when waking: If you need to move your sleeping baby, rest a gentle hand on their chest or tummy first to give them reassurance before you lift them. 
  • Stick to routines: A predictable bedtime routine helps your baby feel secure and might reduce how often they startle. 
  • Get the temperature right: Make sure the temperature of the room your baby is sleeping in isn't too hot or too cold, as being uncomfortable can make babies more restless and prone to startling. 

Does swaddling help startle reflex? 

Absolutely, swaddling can help to soothe a baby’s startle reflex. When done properly and safely, swaddling mimics the feeling of being in the womb, giving babies gentle containment and security that helps them settle.  

The snug wrapping can stop your baby's flailing arms from setting off the Moro reflex or waking them from sleep. 

Why swaddling helps with startle reflex: 

  • Keeps baby's arms tucked in close to their body, reducing how intense the startle response feels 
  • Gives a sense of comfort and security that can help babies sleep for longer stretches 
  • Creates a familiar, womb-like feeling that many newborns find calming 

Safe swaddling guidelines

  1. Always put your baby on their back to sleep when swaddled.
  2. Make sure the swaddle isn't too snug around the hips and legs, they need room to move naturally for healthy hip development.
  3. Stop swaddling as soon as your baby shows any signs of rolling over, which usually happens around 2-4 months.
  4. Choose lightweight, breathable fabrics or a specially designed swaddle suit to prevent overheating.

Stay safe

While swaddling can really help with the startle reflex, remember to stop once your baby shows any signs of rolling, and always stick to safe sleep guidelines.

The startle reflex is just one of many amazing reflexes your newborn has at birth, and watching these automatic responses slowly give way to purposeful movements is one of the special parts of the early months. 

While the Moro reflex can sometimes interrupt sleep or cause a moment of distress, it's temporary and a completely normal part of your baby's development. 

With a bit of understanding and some helpful approaches like swaddling, you can support your baby through this stage and help the whole family get more rest. 

Can the startle reflex come back?

Once the Moro reflex has completely gone (usually by 6 months), it doesn't typically come back. That said, babies and older children will still have normal startle responses to sudden loud noises or unexpected things throughout their lives. These later startle responses are different from the Moro reflex, they're more controlled and don't include that distinctive arm-flinging and back-arching pattern. 

If you notice reflex-like movements returning after your baby has outgrown the Moro reflex, it's a good idea to check in with your GP or child health nurse to rule out any underlying concerns. 

The startle reflex itself doesn't usually get worse as your baby grows. However, you might notice it happening more often during certain times, particularly around 3 months when babies are becoming more alert to their surroundings and may be more easily stimulated. 

Some babies naturally have stronger or more frequent startle reflexes than others, which is usually just down to individual temperament rather than something to worry about. If you think your baby's startling seems excessive, unusually strong, or is happening alongside other concerning symptoms, have a word with your GP or child health nurse for reassurance and advice. 

There's no direct evidence that the startle reflex itself prevents Sudden Infant Death Syndrome (SIDS). However, the startle reflex does show that your baby has a functioning and healthy nervous system, which is important for overall wellbeing. 

The best ways to reduce SIDS risk include placing your baby on their back to sleep, using a firm sleep surface, keeping the cot clear of loose bedding and toys, maintaining a comfortable room temperature, and avoiding overheating. 

Red Nose Australia also recommends room-sharing (but not bed-sharing) for at least the first 6 to 12 months. 

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