The pink-noise machine meant to lull millions of Americans into deeper sleep may actually be doing the opposite: cutting into one of the brain’s most important stages of rest, according to a sleep-laboratory study.
Pink noise is widely marketed as a gentler, more “brain-friendly” way to sleep.
Deeper and softer than the hiss of white noise, often likened to a distant waterfall, it has become a popular way to mask traffic noise, snoring, or barking dogs.
However, in the study, published in the journal Sleep, researchers found that playing pink noise continuously through the night reduced REM sleep by about 15 to 20 minutes—or a 15 percent reduction.
Throughout his scientific career, Dr. Mathias Basner’s research has shown that noise can be detrimental to both sleep and health.
“It seemed counterintuitive to me to put a noise source into your bedroom,” Basner, lead author of the study and a professor of psychiatry at the University of Pennsylvania Perelman School of Medicine, told The Epoch Times.
To the sleeping brain, the findings suggest, a soothing sound may not be a neutral sound.
Reduced Deep and REM Sleep
The seven-night University of Pennsylvania sleep-laboratory study involved 25 healthy adults; none had diagnosed sleep disorders or regularly used sound machines.
Lights went out at 11 p.m., and participants were awakened at 7 a.m. each morning. Each night, researchers exposed participants to different soundscapes and monitored their effects on brain activity.
The different soundscapes were: near silence, aircraft noise, pink noise, pink noise with aircraft noise, or aircraft noise while wearing foam earplugs.
Throughout the night, the team monitored brain waves, eye movements, breathing, muscle tone, and heart activity. Participants were also surveyed on their mood and fatigue each morning.
Complete silence was the most restorative.
Environmental aircraft noise alone mainly disrupted deep sleep, reducing it by an average of 23.4 minutes—roughly a 20 percent loss—and increasing brief awakenings and time spent awake during the night.
Pink noise caused reductions in both deep and REM sleep.
REM and deep sleep states are both important for rest and brain health. While REM supports mood regulation and mental focus, deep sleep is important for memory and cognitive function.
Participants who were exposed to aircraft noise or pink noise both reported their sleep quality and mood to be worse the next day.
Listening to pink noise with environmental noise—which is how it is used in real life to mask sound disturbances—caused the greatest reductions in both deep and REM sleep.
“You got the deep sleep reduction from the environmental noise, you got the REM sleep reduction from the pink noise, and then you got more superficial sleep and more awake time,” Basner said. “The combination kind of wreaked havoc on the sleep.”
Earplugs, by contrast, did far more to protect sleep. Using foam earplugs restored about 20 minutes of combined deep and REM sleep lost to environmental noise.
“Of the deep sleep that was lost due to the environmental noise events, 73 percent was recuperated by wearing earplugs,” Basner said.
At moderate noise levels, sleep on earplug nights looked very similar to quiet control nights, and participants barely reacted to most noise events.
What Pink Noise Did to Sleep
When played alone at 50 decibels—about the volume of a quiet conversation or low refrigerator hum—pink noise reduced REM sleep by an average of 18.6 minutes, with that time largely replaced by lighter sleep. Total time in deeper sleep also dropped, while time in lighter sleep and awake time edged up.
“Pink noise both prevents initiation of REM sleep and also the maintenance of REM sleep,” Basner said.
Losing 20 minutes of REM sleep may not sound dramatic in a single night, Basner pointed out, but those losses can accumulate night after night, especially for adults who are already sleeping less than the recommended seven hours.
It is not yet clear why pink noise interferes with REM sleep. Basner noted that even during sleep, our ears and brain are still working in the background, taking in sounds and turning them into signals the brain has to process. He said he suspects that constant sound may make it harder for the brain to enter and remain in REM sleep, keeping us in deeper stages of rest.
Why Lost REM Sleep Matters
REM sleep does some of the brain’s most important overnight work—it helps process emotions and store certain kinds of memories.
“REM sleep is very important for emotional regulation and [disrupted REM sleep] has been implicated in post traumatic-stress disorder,” Basner said.
Scientists have also found connections between disrupted REM sleep and brain conditions such as Parkinson’s disease and some forms of dementia. It’s not yet clear whether poor REM sleep causes these issues or shows up as an early warning sign, but the link is strong enough to raise concern.
Even small losses can add up. Missing about 20 minutes of REM sleep each night means less time in the stage that supports emotional balance and learning. And because REM sleep mostly happens in the early morning hours, people who cut their sleep short often don’t get a chance to make up for what they’ve missed.
Children May Be Especially Vulnerable
The study did not include babies or children, but Basner said he worries that the findings may be particularly relevant for them. Newborns spend about half of their sleep in REM, an important stage for brain development in early childhood, compared with roughly one-quarter in adults. And white-noise machines are a common sleep aid that parents use because they mimic the whooshing sounds of the womb and also mask household disturbances.
“So when we are finding that the predominant feature of pink noise—standing in for other kinds of broadband noise—is a REM sleep reduction, both preventing initiation and maintenance of REM sleep, and you put that next to your newborn’s bed, I would say that might not be the best for their brain development, even though we haven’t studied babies directly,” Basner said.
No Obvious Next‑Day Damage
Despite the changes in REM and deep sleep, researchers did not find large differences in standard next-morning cognitive tests or cardiovascular measures. Reaction times and attention scores remained similar, and heart measures showed no immediate harm.
However, participants consistently reported worse sleep quality, alertness, and mood after nights with environmental noise or pink noise than after quiet nights. Sleep is very important for long-term health, and many of the health effects linked to disrupted sleep—including depression, high blood pressure, and metabolic disease—emerge gradually, after months or years of disrupted sleep.
For people who already rely on sound machines, Basner doesn’t say that everyone has to stop. Instead, his study suggests using them with care: Keep the volume as low as possible, avoid placing speakers right next to your head or your child’s crib, and consider using sound mainly to fall asleep rather than all night.
And if outside noise is the real problem, he said, simple measures such as earplugs, better windows, and insulation are more likely to protect sleep more effectively than adding yet another layer of sound.
“Sleep is a huge market,” Basner said. “There are lots of companies out there that claim they have scientific evidence for their product. If you take a deeper dive, there’s very little—and sometimes, as our study shows, there may even be harm.”