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Why Do Babies Flail Their Arms? All About Newborn Reflexes

Newborns are full of snuggles, wails, and wrinkly skin. They also have a bunch of funny movements. For example, parents may wonder why babies flail their arms out when surprised. These movements relate to the developing nervous system. Newborn reflexes are involuntary movements or positions. And, they begin to develop even before a baby is born at full term. Today’s post reviews some of the more important newborn reflexes, including arm flailing. Parents may find it helpful to know what a doctor is looking for during the newborn exam. And, hopefully they can find reassurance when they see their own baby showing off these same newborn reflexes.

So, why do babies flail their arms? I’ll cover that one first. Then, read on for a review of a few of the other newborn reflexes.

Before I go any further, please note this is general information. If you’re ever wondering if a specific movement is normal, please ask your baby’s pediatrician! Taking a short video of the movement is helpful. This way you don’t have to rely on your baby “performing” when they see their doctor.

Moro Reflex

Also called the startle reflex, this can look like arm flailing. In other words, this is the normal newborn reflex families refer to when they describe their baby flailing their arms. 

The movement includes both arms quickly going out as if preparing for a big hug. Then the hands quickly come back towards each other. Often, it comes with a cry. The legs are also involved.

When does it happen?

Doctors test for this reflex specifically when they examine a newborn. They expect the reflex and movement to be roughly symmetric. The arms move out and in at about the same intensity. A parent may see the Moro reflex if a baby is surprised (startled) when the baby isn’t swaddled. The baby may move their arms and legs out and then back in and cry. 

If the baby is on their back and someone lifts both their hands and then releases the hands, this may also trigger this reflex. 

How long does it last?

By age 5-6 months, most babies have outgrown this arm-flailing reflex. After this age, they won’t respond the same way to a startle or being partially lifted by their arms. 

Palmar grasp

For many parents, the palmar grasp reflex is intensely emotional. The palmar grasp refers to the newborn reflex that takes place when an object (like an adult finger) is placed in the baby’s palm. When this happens, the newborn grabs the finger. If the adult attempts to move away, the baby’s grip tightens. 

We can see the primitive and safety benefits of this “palmar grasp.” The baby literally holds on to their parent. 

From a personal point of view, having witnessed countless parents meet their new babies for the first time, it’s this moment of the parent’s finger in their baby’s hand that seems to further awaken a bond. And, to be clear, even though it’s a primal neurological reflex, I think it can also be a beautiful moment of connection. 

How long does it last?

By age 2-3 months, most babies don’t grasp an adult’s finger as consistently and reflexively. 

Rooting Reflex

When something touches a baby’s cheek or corner of their mouth, they “root.” The baby will turn their head towards the touch and open their mouth, looking for something to suckle. They often move their tongue out as if preparing to feed as well. This has benefits of helping babies latch and feed. And yes, sometimes the “something” that stimulates the reflex is their own hand. So, the rooting reflex can lead to babies sucking on their own hand or fingers.

(Rooting is different than sucking, discussed below).  

How long does it last?

After about age 1 month, the rooting reflex is less obvious. It gradually disappears by age 4-6 months.

Of note, older adults who have certain types of brain damage (including dementia affecting the frontal lobe) may “regain” their rooting reflex. 

Sucking reflex

This time, the name describes the reflex perfectly. Unlike rooting where touching the cheek or corner of the mouth stimulates a movement, sucking happens when the roof of the baby’s mouth is touched. As a physician, I check this with a gloved finger. This entire reflex involves the series of movements (lips and tongue included) that allow for sucking then swallowing.

Importantly, the whole coordination of sucking, swallowing and breathing doesn’t develop until about 34 weeks of gestation. I mention this because it can help explain some of the challenges of babies born prematurely. It’s worth remembering this timeline when we think about expectations for babies to feed well without extra help.

Tonic Neck, also known as Fencer’s Position

Tonic neck reflex or “fencer’s position”

This reflex actually looks like a specific position that remains after the movement takes place. Many describe it as a fencer’s “en garde” position. Here is how it happens. A baby is laying on their back. A parent (or examining doctor) gently turns the baby’s head to one side. Then, the reflex takes place: the arm the baby is facing reaches towards the direction the baby is looking. The opposite arm bends at the elbow. 

Some theories suggest this is important for babies to help develop eyesight and hand-eye coordination as they look at their own hand.

How long does it last?

The fencer’s position reflex is present until about age 6-7 months. 


As newborns grow and develop, many of their movements become much more intentional. For the first few months, though, they rely a lot on these so-called primitive newborn reflexes. From bonding to feeding, their nervous system is helping! There are other newborn reflexes. The ones listed here are among the most important and talked about. As always, questions about your baby are best answered by the pediatrician examining your baby.

If you’d like a paperback or ebook of short answers to the most commonly asked questions about newborns, find my booklet here on Amazon. For monthly info and tips on kids’ health, sign up for my free newsletter below.

About the Author: Maya Mahmood, D.O., F.A.A.P. is a board-certified pediatrician and mom. She is passionate about parents having evidence-based information to help their families be healthier.

Palmar grasp photo by Anastasia Zhenina on Unsplash. Fencer’s position photo by Flávia Gava on Unsplash.

over image of adult hands holding a baby's hands is the text "why do babies flail their arms? 5 Newborn Reflexes Explained."

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