Baby sleep
Why white noise calms babies
A crying baby can go quiet within moments of hearing a steady hush. Here are the main reasons parents and researchers give.
White noise is thought to calm babies for several reasons: it resembles the constant sound they heard in the womb, it covers sudden noises that startle them, and a steady sound gives the brain less to react to. None of these is proven as the single cause.
The womb was never quiet
Before birth, a baby lives in constant sound: the mother's heartbeat, blood moving through vessels, breathing, digestion and voices muffled through fluid. Measurements of the sound inside the womb vary between studies, but they agree that it is mostly low-pitched and always present. After birth, a newborn goes from that environment into a much quieter and sharper world. A steady hush bridges the gap.
This is the idea behind sounds such as womb, heartbeat and brown noise. Do not copy the loudness of the womb though: a safe sleep sound should be much quieter than that. See how loud should baby white noise be.
It covers the sounds that startle
Newborns have a startle reflex, and sudden sounds can set it off. A steady sound raises the baseline, so a door closing or a dog barking stands out less. That is called masking, and it is the best-understood reason sound helps. Read more in how white noise works.
Constancy is calming
A sound that never changes asks nothing from the brain. There is no melody to follow, no words to understand and no surprise. For a tired baby who is easily over-stimulated, that sameness can be restful.
The "shush" instinct
Parents have used shushing for centuries. Harvey Karp, in his well-known "5 S" method for fussy babies, includes loud, rhythmic shushing as one step, alongside swaddling, side or stomach position while holding, swinging and sucking. White noise is a way to deliver the shush hands-free. For a baby on their sleeping surface, the safe position is always on the back.
Learned association
A baby who hears the same sound at every sleep begins to link it with sleep. After a few weeks the sound itself becomes a cue, like a lullaby or a bath. This is useful, and it is also why some children want it for a long time.
What is not proven
No study has proven that white noise works because of any one of these. Babies also differ: some love it, some are indifferent and a few dislike it. If your baby does not seem to benefit, that is normal. See what the research says.
Frequently asked questions
Why does my baby stop crying with a hair dryer or vacuum on?
These sounds are loud, wide and steady, which can cover other noise and feel like the constant sound from before birth. A recording at a low volume gives the effect without the machine. See hair dryer sound and vacuum sound.
Is the womb really as loud as a vacuum?
Some measurements have been in a similar range, but results vary and the sound is mostly low-pitched and muffled. That is not a reason to play it that loudly. A baby's sleep sound should be much quieter.
This page is general information, not medical advice. Talk to your pediatrician about your baby's sleep and hearing, and follow current safe sleep guidance.