Sound machines have not been directly proven to cause speech delays, but there are real reasons for concern. The combination of how infant hearing works and how loud these devices can get creates conditions that could interfere with language development, especially with prolonged or high-volume use. The good news: simple adjustments to volume, placement, and duration can minimize the risk while preserving the sleep benefits.
What the Research Actually Shows
No large-scale study has definitively concluded that sound machines cause speech delays in otherwise healthy children. However, the evidence we do have points in a worrying direction. A 2024 scoping review of white noise exposure during sleep found that these machines can exceed 91 decibels on maximum volume, which surpasses occupational noise safety limits for a two-hour adult work shift. Animal studies consistently show that continuous moderate-intensity white noise disrupts early auditory development, and human data generally supports those findings.
Researchers at Children’s Hospital of Philadelphia examined the maximum output levels of popular infant sleep machines and concluded that continual nightly use could affect hearing, speech, and language development. A separate review published in Noise Health noted that prolonged exposure to loud noise devices can result in permanent hearing loss and developmental delays. The American Academy of Pediatrics has warned that repeated loud noise exposure may be associated with impaired learning and memory functions in addition to progressive hearing loss.
Why Babies Are More Vulnerable Than Adults
The core issue isn’t just volume. Babies process sound fundamentally differently than adults do. When adults hear a tone in the presence of background noise, they can tune in to the relevant frequency and ignore the rest. Infants can’t do this. Studies show that babies listen across a broad, unselective range of frequencies, which means even noise that doesn’t directly overlap with speech sounds can still interfere with what they hear. In one experiment, six-month-olds needed sounds to be about 10 decibels louder to detect a tone in background noise compared to quiet conditions, while adults showed no difference.
This matters enormously for speech. When researchers tested whether infants could tell apart different speech sounds while remote-frequency background noise played (sounds that didn’t even overlap with the speech frequencies), roughly half of the babies failed to discriminate between the phonemes. The same babies could distinguish those sounds just fine in quiet. Researchers believe this happens because listening to speech against competing noise is far more cognitively demanding for infants, likely due to immature selective attention. Babies younger than 10 months simply haven’t had enough listening experience to separate relevant sounds from background noise.
How Constant Noise Could Affect the Brain
Beyond masking speech sounds, there’s evidence that white noise changes how the brain’s auditory system wires itself. One neurological study found that white noise reduced connectivity between the primary auditory cortex and motor cortex, along with other brain regions. This reduction was most prominent in the right hemisphere’s primary motor cortex. These connections matter because the auditory and motor systems work together during speech development: babies need to link the sounds they hear with the mouth movements that produce them.
The concern isn’t that a sound machine will immediately harm your baby’s brain. It’s that during a critical window of auditory development, constant noise exposure may slow down the process of learning to distinguish and categorize the speech sounds that form the foundation of language.
The Sleep Benefit Is Real
Sound machines became popular for a reason. White noise mimics the constant ambient sound of the womb, and after birth, exposure to these familiar rhythms calms infants. Research on preterm babies shows white noise reduces crying, lowers energy expenditure, and helps newborns adapt to life outside the womb. Better sleep supports growth, mood regulation, and yes, cognitive development too.
This is the tradeoff parents face. A baby who sleeps poorly may also experience developmental challenges, so the goal isn’t necessarily to eliminate sound machines entirely. It’s to use them in ways that capture the sleep benefit without the auditory risks.
How to Use a Sound Machine Safely
The AAP recommends keeping the volume below 50 decibels, roughly equivalent to a soft conversation. Most parents set their machines too loud. If you have to raise your voice to talk over it, it’s far too high.
- Keep it at least two feet from the crib. Distance reduces the sound pressure reaching your baby’s ears significantly. Placing the machine across the room rather than on the crib rail makes a meaningful difference.
- Turn it off once your baby falls asleep. There’s no benefit to running white noise all night. Use a timer function so the machine shuts off after 30 to 60 minutes.
- Choose a machine with adjustable volume. Avoid models with only one or two settings. You want fine control to keep it at the lowest effective level.
- Skip it during awake time. When your baby is alert and interacting with you, they need a clear auditory environment to hear speech sounds, practice distinguishing phonemes, and connect your voice with your facial expressions.
The pattern that raises the most concern is a sound machine running at high volume, positioned near the crib, playing continuously through every nap and nighttime sleep for months on end. That creates the kind of prolonged, moderate-to-high-intensity exposure that animal and human studies flag as problematic. Used briefly at low volume to help a baby fall asleep, the risk profile looks very different.
When Background Noise Becomes a Bigger Problem
Sound machines aren’t the only source of constant background noise in a baby’s environment. Television left on in the background, loud fans, and busy household noise all contribute to the same masking effect. If your baby spends most of their waking hours in a noisy environment and then sleeps with a sound machine running all night, the cumulative result is very little quiet time for their auditory system to practice processing speech.
Babies learn language by hearing it clearly, repeatedly, and in context. They need stretches of relative quiet where your voice is the dominant sound. If you’re concerned about your child’s speech development, reducing overall background noise during interactive, awake periods is likely just as important as what happens with the sound machine at bedtime.