When Do Babies Lose the Startle Reflex

What the startle reflex is

The Moro reflex, better known as the startle reflex, is the dramatic one. The AAP describes it precisely: "If your baby's head shifts position abruptly or falls backward — or if he is startled by something loud or abrupt — he will extend his arms and legs and neck and then rapidly bring his arms together. He may even cry loudly."

It is not a sign of fear or distress in the ordinary sense. It is an involuntary reflex that every healthy newborn has, and it is one of the things checked in the newborn physical examination.

When it goes

The AAP gives the timing plainly: the Moro reflex "is present in varying degrees in different babies, usually peaks during the first month and starts to disappear after about two months".

Two words in that sentence are doing important work. "Varying degrees" means some babies have a huge, whole-body startle and others barely twitch, and both are normal. "Starts to disappear" means it fades rather than switching off — a three-month-old may still startle occasionally, particularly when tired or when put down quickly.

The other newborn reflexes and their timings

The AAP describes several, and the timings differ, which is why "when do reflexes go" has no single answer:

• Rooting — turning the head towards a stroked cheek. This one becomes voluntary behaviour rather than simply vanishing, and the AAP notes babies later use rooting, sucking and hand-to-mouth movements to console themselves.
• Sucking — present before birth; the AAP describes it becoming "a skill that they all manage well" with practice.
• Tonic neck reflex, or the fencing posture, where a baby's arm straightens on the side the head is turned towards. The AAP says it "disappears at five to seven months of age" and warns it is subtle and may not be seen at all.
• Grasp reflex — a baby gripping a finger placed in the palm, or curling the toes when the sole is stroked. The AAP cautions that although the grip can feel strong enough to hold a baby's weight, "he has no control over this response and may let go suddenly".
• Stepping — a baby held upright with feet on a surface placing one foot in front of the other. The AAP says this "will disappear after two months, then show up again toward the end of the first year as the learned behavior of walking".

The HSE describes the same period from the other side: a one-month-old "is startled by loud noises" and "will begin to loosen their tight fists"; by two months the hands are "loose and not in fists for about half of the time"; by three months, "most of the time". Fists opening is the reflex grip giving way to voluntary use.

What the fading actually means

Reflexes are run by the more primitive parts of the nervous system. As the brain matures, voluntary control takes over and the automatic version is suppressed. So the reflexes disappearing is not a loss; it is the replacement of an automatic response with a chosen one. The stepping reflex is the clearest illustration — gone at two months, back at the end of the year as actual walking.

What it means for sleep

A strong startle wakes babies, which is why the reflex comes up so often in conversations about sleep. Swaddling is the traditional response, and it needs to stop before a baby can roll. This is not a reason to keep a baby wrapped: the reflex fades on its own timetable regardless of what anyone does about it.

If your baby was born early

Reflexes appear and fade on a schedule tied to development, so use corrected age. A baby born two months early is at one month corrected when they turn three months, and a startle at that point is entirely expected. The AAP advises using adjusted age for tracking development until two years.

The thing to report

Not the timing. The symmetry. The AAP is explicit: "Both the Moro and tonic neck reflexes should be present equally on both sides of the body. If you note that the reflex seems different on one side, or that the baby moves one side of the body better than the other, tell your pediatrician."

NICE says the same thing in guideline language, listing "unusual fidgety movements or other abnormalities of movement, including asymmetry or paucity of movement" and "abnormalities of tone, including hypotonia (floppiness), spasticity (stiffness) or dystonia (fluctuating tone)" among the possible early motor features of cerebral palsy, and recommending urgent assessment for children at increased risk who show them.

A reflex that persists well beyond its window is also worth mentioning — a strong Moro at six months, or fists still tightly clenched at four months, are observations a clinician can act on. The HSE lists a baby who does "not grasp objects when placed in their hands" at two and four months among its reasons to contact a GP or public health nurse.

And as always: contact someone if your baby loses a skill they had before, at any age.

What a startle is not

It is not a sign that a baby is anxious, and it is not caused by anything a parent did. A baby who startles when put down in the cot is showing a normal reflex response to the change in head position, not an objection to being put down. Lowering a baby bottom first, keeping a hand on them for a moment after they land, and moving slowly all reduce how often it fires — but none of that is treating a problem.

It is also not the same as the jerky twitching that many babies do while falling asleep, or the brief tremors of a hungry or cold newborn. Those are separate phenomena. Persistent tremors, jerking that continues while a baby is held firmly, or any episode where a baby becomes stiff, blue or unresponsive is a different matter and needs urgent medical assessment rather than reassurance from an article.

Why the newborn examination checks them

Reflexes are one of the few ways to test a very young nervous system that cannot yet do anything voluntarily. Their presence, their strength and above all their symmetry give a clinician information no milestone chart can provide at that age, which is why they feature in the routine newborn physical examination and in follow-up checks for babies born early or unwell.