What Is the Startle Reflex and Why Does it Matter?
Have you ever noticed your Baby suddenly throw their arms out wide, arch their back, or look startled by a noise, movement, or change in position?
This is called the Startle Reflex (often called the Moro Reflex). While it can sometimes surprise parents, it is a normal and important part of Baby's early nervous system development.
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 how primitive reflexes work is to think about what happens when you accidentally touch a hot stove. Your body reacts before you even have time to realize that you are touching something hot – it is automatic and you just react to the stimulus of the hot surface.
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.
What the Startle Reflex Helps Baby Learn
The purpose of the Startle Reflex is to help keep Baby safe. It also gives Baby a way to communicate to their caregivers that something feels unexpected, or uncomfortable.
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.
As Baby's brain develops and gains more control over movement, the Startle Reflex gradually becomes less sensitive. Baby can handle more movement, more noise, and more changes in position before the reflex is triggered.
This process is called reflex integration. As Baby develops new movement skills and body awareness, the brain gains more control over movement and the reflex gradually fades away.
What Happens If the Startle Reflex Stays Active?
In some cases, the Startle Reflex does not fully integrate. This is called a retained primitive reflex. When this happens, loud noises, sudden movements, or unexpected situations may continue to trigger the nervous system long after infancy.
Children who have a retained Startle Reflex may be more likely to experience:
Anxiety
Bossiness or a strong need to control situations
Emotional outbursts
Balance challenges
Excessive worry about new tasks or new people
Remember, the purpose of the Startle Reflex is to keep Baby safe.
For children with a retained Startle Reflex, new experiences, people, and situations may become stressful. The child may work hard to control their environment because their nervous system is constantly looking for safety.
How Can I Support My Baby's Development?
When parents understand the purpose of the Startle Reflex, they can add simple activities to their day that give Baby every opportunity to integrate the Startle Reflex naturally.
Providing opportunities to move, roll, reach, and explore all help Baby build the movement skills and body awareness that support healthy development.
These may include:
Gentle touch and Infant Massage
Tummy time
Dipping Baby backwards as you dance or play together
Encouraging "Dad-style" play where Baby experiences many different positions and movements
Rolling, rocking, and playful movement experiences
Bringing these activities into Baby's day provides valuable input to their growing nervous system and supports healthy development.
Movement is one of the most important ways Baby learns about their body and the world around them. You can learn more in our article, Why Movement Matters Before Milestones, where we explain how everyday movement supports healthy brain and nervous system development.
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/