Have you ever noticed your Baby suddenly throw their arms outward, open their hands, or seem startled by a loud noise or a change in position?
This is Baby's Startle Reflex, also known as the Moro Reflex. Both names are commonly used for this early reflex, but we'll use Startle Reflex throughout this article because it's easier for parents to recognize and remember.
The Startle Reflex is an automatic response that is present from birth and is an important part of early nervous system development.
Understanding why this reflex happens, what it looks like, and how it changes as Baby grows can help you feel more confident about the movements you see during the first few months.
What Are Primitive Reflexes?
Primitive Reflexes help Baby respond automatically to specific movements, noises, and touches. They exist to help Baby interact with their environment before they learn how to move their body on purpose.
The easiest way to understand a reflex is to think about what happens when you accidentally touch something hot. Your hand pulls away before you've even had time to think about it. This is an automatic reflex response.
Baby's primitive reflexes work automatically, too. Although they are different types of reflexes, they also help Baby respond to their surroundings without having to think about what to do.
Some common Primitive Reflexes include:
Rooting Reflex – touch Baby's cheek and they turn toward the touch.
Palmar Grasp Reflex – touch the palm of Baby's hand and they wrap their fingers around yours.
Plantar Reflex – touch the sole of Baby's foot and they curl their toes.
The Startle Reflex is just one of several important Primitive Reflexes that support Baby's early development.
To learn more about how Primitive Reflexes work together and why they matter, please visit Understanding Primitive Reflexes.
Why Is the Startle Reflex Important for Baby?
The Startle Reflex is an automatic protective response to sudden changes in Baby's surroundings or position. It is one of the ways Baby's developing nervous system responds to unexpected sensory information. As Baby matures, this reflex gradually becomes less prominent.
Every time Baby experiences a change in position, movement, or sensory input, their nervous system receives information about the world around them.
The Startle Reflex is activated when Baby experiences a sudden change in position, a loud noise, a bright light, or another unexpected stimulus.
Here are some of the reactions you might see when Baby startles:
Throw their arms outward
Open their hands
Extend their legs
Take a quick breath in
Bring their arms back toward their body
Cry
When Will I Notice the Startle Reflex?
Many parents notice the Startle Reflex most often during the first few months after birth.
It is common to see the Startle Reflex when:
Putting Baby down into their crib
Changing positions during feeding
You accidentally drop something on the floor and it makes a loud noise
Someone suddenly laughs nearby
During sleep transitions
Some Babies startle frequently, while others seem less reactive. Both can be completely normal.
Because every nervous system develops at its own pace, there is a wide range of typical responses.
How Does the Startle Reflex Change Over Time?
Primitive Reflexes are designed to be temporary.
The Startle Reflex usually becomes less noticeable during the first few months and typically disappears by around 4 to 6 months of age. Every Baby develops at their own pace, but if the reflex remains pronounced beyond this period, or appears noticeably different on one side, it's worth discussing with Baby's healthcare provider.
As Baby's brain develops, they gain greater control over their movements and become more comfortable with everyday changes in position and sensory experiences.
This gradual change is called reflex integration. As Baby develops new movement skills and body awareness, the Startle Reflex becomes less prominent and eventually disappears.
What Happens If the Startle Reflex Stays Active?
In some children, the Startle Reflex may remain active beyond the age when it would normally disappear. This is called a retained primitive reflex.
When a child continues to show strong startle responses, everyday experiences such as loud noises, sudden movements, or unfamiliar situations may feel overwhelming.
Some children who are particularly sensitive to unexpected experiences may:
Become easily startled or overwhelmed by loud noises
Feel anxious or uncomfortable in unfamiliar situations
Have difficulty adjusting to unexpected changes
React strongly when something doesn't go as expected
Try to control their surroundings to make things feel more predictable
Remember, the Startle Reflex is a protective response.
A child who seems controlling, worried, or easily upset may be trying to manage experiences that feel unpredictable or uncomfortable.
These behaviors can have many different causes and do not, by themselves, indicate a retained Startle Reflex. However, understanding how a child's nervous system responds to their surroundings can help parents approach their behavior with greater curiosity and understanding.
To learn more about how primitive reflexes may continue to influence development beyond infancy, visit our Retained Primitive Reflexes page.
How Can I Support My Baby's Development?
Everyday touch, movement, and play provide opportunities for Baby to explore their body and surroundings as their nervous system develops.
Gentle Infant Massage, supervised tummy time, reaching, rolling, rocking, and playful movement can all be part of Baby's daily routine.
Follow Baby's cues, choose movements appropriate for their developmental stage, and give them time to enjoy each new experience.
To learn more about the importance of early movement, visit our article Why Movement Matters Before Milestones.
Find Out More at Best Beginnings
Understanding Primitive Reflexes can help you appreciate how movement, touch, and everyday experiences influence Baby's growing nervous system.
At Best Beginnings, we've created simple, practical activities that parents can use at home to support Baby's development through touch, movement, rhythm, and play.
Inside the Best Beginnings Online Baby Massage and Movement Program you'll find:
A complete Infant Massage program with step-by-step video instruction
A movement guide filled with fun ways to play with Baby
Easy-to-understand information about Primitive Reflexes and their role in development
Activities that support the Rhythm and Sound pillar
Ideas for encouraging Sensory Play using everyday items
If you'd like to learn more about supporting Baby's development through Baby Massage, movement, Primitive Reflexes, rhythm, and sensory play, visit our Learn Baby Massage page to discover the Best Beginnings Online Baby Massage and Movement Program.
References
Goddard Blythe, S. (2005). The well balanced child: Movement and early learning. Hawthorn Press.
Pattnaik P, Al Khalili Y. Moro Reflex. [Updated 2025 Aug 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK542173/