Pink Noise Sleep Machines May Disrupt Restorative REM Sleep, Study Finds
When sleep proves elusive, countless individuals turn to sound machines that emit steady, non-looping audio like pink noise, rainfall, or fan sounds to mask bothersome background noises and foster a tranquil atmosphere. However, a groundbreaking study from the University of Pennsylvania's Perelman School of Medicine indicates that pink noise-producing devices might actually be interfering with the most restorative phases of sleep for their users.
Unexpected Impact on REM Sleep
The research team discovered that pink noise significantly reduced REM sleep, the stage most closely linked with dreaming. In a striking contrast, simply wearing earplugs demonstrated far greater effectiveness in shielding participants from traffic noise and safeguarding 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," explained Mathias Basner, the study's lead author and a professor of psychiatry at the Perelman School of Medicine. Basner further noted to HuffPost that when pink noise was played concurrently with external noise, sleep quality deteriorated even more markedly.
Participants experienced increased nighttime awakenings, took longer to fall back asleep after disruptions, and generally spent less time in the crucial REM stage.
Why REM Sleep Matters
"This matters because REM sleep is important for memory consolidation, emotional processing, and has been implicated in neurodegenerative diseases like Parkinson's," emphasized Basner, a leading authority on the health impacts of noise.
Children devote substantially more time to REM sleep than adults, potentially making them especially vulnerable to its disruption, Basner pointed out. The "soothing" sounds from sleep machines could be particularly problematic for children, given that REM sleep constitutes about 50% of an infant's sleep period, compared to 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 advised.
Understanding Pink Noise
Pink noise delivers a balanced, steady background hum, presenting a gentler alternative to white noise. While both encompass all audible frequencies, white noise maintains equal intensity across all frequencies, resembling harsh television static. Pink noise diminishes the higher frequencies, yielding a smoother, more natural sound often likened to steady rainfall, wind rustling through trees, or waves gently crashing on a shore.
Having dedicated his scientific career to examining the detrimental effects of traffic noise on sleep, Basner expressed surprise that millions intentionally introduce a noise source into their bedrooms hoping to sleep better.
"I have not used these sound machines myself and I don't know why they are so popular," he admitted. "Subjectively, they must give users some relief, otherwise why would they be so popular?" Despite their widespread use, scant scientific evidence exists either supporting or opposing broadband noise—a gap that motivated Basner and his team to investigate further.
"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 clarified.
Study Methodology and Limitations
To conduct the study, Basner and his colleagues monitored 25 healthy adults aged 21 to 41 in a controlled sleep laboratory. Participants were afforded eight-hour sleep opportunities over seven consecutive nights. None suffered from sleep disorders or regularly used sound to aid sleep at the study's outset.
During the research, participants rested under several varying conditions:
- Exposure to aircraft noise
- Pink noise alone
- A combination of aircraft noise and pink noise
- Aircraft noise while wearing earplugs
Each morning, sleepers completed cognitive tests and health questionnaires designed to evaluate sleep quality and alertness.
Basner acknowledged the study's limitations, most notably the inability to investigate long-term noise machine use effects.
"It could be that people habituate to the negative effects of broadband noise with long-term use," he speculated. "It could also be that the effects are getting worse. We want to do more studies on it."
Practical Recommendations for Sleepers
For now, individuals struggling with sleep might consider trying sleep earplugs before hastily purchasing a sound machine.
If you find that a white or pink noise machine assists your sleep, experts strongly advise keeping the volume low, particularly 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, previously told HuffPost.
For adults, the sound of a conversation registers about 60 decibels, so experts recommend setting devices to that level or slightly higher.
