When sleep doesn’t come easily, many people turn to sound machines, which play steady, non-looping audio — such as pink noise, rainfall or fan sounds — to block out annoying background noises and create a calming environment.
But a new study out of the University of Pennsylvania’s Perelman School of Medicine suggests that pink noise-producing machines may actually be disrupting the most restorative stages of sleep for users.
The researchers found that pink noise reduced REM sleep, the stage of sleep most associated with dreaming. In contrast, simply wearing earplugs was much more effective at shielding people from traffic noise and protecting their overall sleep quality.
“Both the unexpectedly strong reduction in REM sleep from pink noise and the good efficacy of earplugs were somewhat surprising to us,” said Mathias Basner, the lead author of the study and a professor of psychiatry at the Perelman School of Medicine.
When pink noise was played alongside outside noise, sleep quality declined even more, Basner told HuffPost.
People spent more time awake during the night, took longer to fall back asleep after a disruption and generally spent less time in REM sleep.
“This matters because REM sleep is important for memory consolidation, emotional processing, and has been implicated in neurodegenerative disease like Parkinson’s,” said Basner, a leading expert on the health effects of noise.
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Children spend significantly more time in REM sleep than adults, which may make them especially sensitive to its disruption, Basner said.
The “soothing” sounds from sleep machines may be especially disruptive for children, since REM sleep makes up about 50% of an infant’s sleep period compared with roughly 20% for older children and adults.
“This suggests that REM sleep is critical during early developmental stages, so we’d caution against the indiscriminate use of broadband noise in the bedroom of newborns and toddlers,” Basner said.
What is pink noise?
Pink noise provides a balanced, steady background hum, making it a gentler alternative to white noise. While both contain all audible frequencies, white noise has equal intensity across all frequencies, sounding like harsh TV static.
Pink noise reduces the higher frequencies, creating a smoother, more natural sound. It’s often compared to steady rainfall, wind moving through trees or rustling leaves, or waves rolling onto a beach.
Having spent his scientific career studying the harmful effects of traffic noise on sleep, Basner said he was surprised to discover that millions of people intentionally add a noise source to their bedrooms in hopes of sleeping better.
“I have not used these sound machines myself and I don’t know why they are so popular,” he said. “Subjectively, they must give users some relief, otherwise why would they be so popular?”
Despite the machines’ popularity, there’s little scientific evidence for or against broadband noise — a gap that prompted Basner and his team to take a closer look.
“The primary reason people use them is masking ― or drowning out other sounds that intrude into our bedroom ― but what we found is that broadband sounds could also disrupt our sleep itself,” he said.
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“If you find that a white or pink noise machine helps you sleep, it’s best to keep the volume low, especially in a child’s room.
How’d researchers conduct this study?
To carry out the study, Basner and his team monitored 25 healthy adults, ranging in age from 21 to 41, in a controlled sleep laboratory. Participants were given eight-hour sleep opportunities over seven consecutive nights. None of the participants were experiencing sleep disorders or regularly using sound to help them sleep at the time of the study.
During the study, participants rested under a few varying conditions. These included exposure to aircraft noise, pink noise alone, a combination of aircraft noise and pink noise, and aircraft noise while wearing earplugs. Each morning, the sleepers completed cognitive tests and health questionnaires designed to assess sleep quality and alertness.
The study has some limitations, according to Basner, the most notable being that they didn’t get to investigate effects on long-term use of noise machines.
“It could be that people habituate to the negative effects of broadband noise with long-term use,” he said. “It could also be that the effects are getting worse. We want to do more studies on it.”
Some takeaways for sleep machine users
For now, troubled sleepers may want to look into getting some sleep earplugs before rushing to buy a sound machine.
If you find that a white or pink noise machine helps you sleep, it’s best to keep the volume low, especially in a child’s room.
“Typically a decibel volume for children and infants would be 50 decibels or lower to minimize any potential harm associated with it,” David Neubauer, a sleep expert at Johns Hopkins Medicine in Baltimore, told HuffPost previously.
For adults, the sound of a conversation is about 60 decibels, so that, or a little higher, is what experts recommend setting your devices to.
