PHILADELPHIA — A new study from researchers at the University of Pennsylvania suggests that pink noise, often touted as a soothing aid for better sleep, might actually be doing more harm than good by disrupting key stages of rest. Published Monday in the journal Sleep, the research involved 25 healthy adults spending seven nights in a controlled sleep lab, where they were exposed to various sound conditions including pink noise, environmental noises, and silence. The findings challenge the growing popularity of noise machines designed to mimic natural sounds like rain or ocean waves, raising questions about their long-term effects on sleep quality.
Pink noise, characterized by its emphasis on lower frequencies, produces a deeper, more rumbling static compared to the even-toned white noise. It's frequently used in apps and devices to promote relaxation and drown out distractions. However, the study found that while pink noise could mask some disruptive sounds, it significantly reduced the time participants spent in rapid eye movement (REM) sleep, a stage essential for mood regulation and cognitive function. On average, participants lost 18.6 minutes of REM sleep per night when exposed to pink noise alone.
The experiment took place in a sleep lab at the University of Pennsylvania, with lights out at 11 p.m. and wake-up at 7 a.m. each night. None of the 25 participants, who were mostly younger women without sleep disorders or habitual use of sound machines, had prior experience sleeping in the facility. Conditions varied nightly: no noise, environmental noise only (ranging from traffic hums to intense sonic booms), pink noise alone, a mix of both at different decibels, or environmental noise with earplugs. Sleep stages were monitored throughout, including light sleep, deep Stage 3 sleep, and REM.
Environmental noise proved particularly disruptive to deep sleep, cutting Stage 3 duration by an average of 23.4 minutes per night. This stage is crucial for physical restoration, memory consolidation, and overall cognitive health. Lead author Dr. Mathias Basner, a professor of psychiatry at the University of Pennsylvania Perelman School of Medicine, noted the unexpected impact of pink noise on REM. "There have been studies that have reported the REM sleep reduction already," Basner said. "Research has been there, but it has been neglected, and we kind of uncovered that again."
Before and after each sleep session, participants underwent physiological tests, cognitive assessments, and surveys on mood and fatigue. The cumulative effect of even small nightly losses could be substantial, according to Basner. "You may be only losing 10 minutes that night, but then across the week, it’s 70 minutes, and across a year, it’s 52 times 70 minutes," he explained, highlighting how chronic disruptions might accumulate over time.
The study didn't examine effects on children or infants, but Basner cautioned against using noise machines for younger sleepers. Newborns spend about half their sleep in REM, compared to roughly 25 percent for adults, making any reduction potentially more severe. "For adults who don’t get the recommended seven hours of sleep per night, each minute of lost REM sleep matters," Basner said. "I wouldn’t discount it as, you know, ‘It’s negligible and it doesn’t affect me.’"
While the exact mechanism remains unclear, Basner speculated that the constant auditory input from pink noise might inhibit natural brain processes during REM. Interestingly, pink noise did help participants ignore traffic sounds better than silence, though earplugs outperformed it in blocking environmental disturbances entirely. This suggests a trade-off: while it masks some noises, it introduces its own interference.
Dr. Rafael Pelayo, a clinical professor in the division of sleep medicine at Stanford University School of Medicine, offered a balanced perspective on the results. He pointed out that the lab setting might not reflect real-world sleeping habits. "The need for sleep is biological, but the way we sleep is learned," Pelayo said, noting that people often adapt to annoyances like a partner's snoring over time.
Prior research on pink noise has been inconsistent, with some studies praising its potential benefits for memory enhancement and sleep onset, while others found neutral or negative effects. The current study's small sample size of 25 participants and short seven-night duration are notable limitations. It's possible that longer exposure could lead to habituation, where the brain adjusts and sleep patterns normalize. Additionally, the environmental noises used — including jets, helicopters, and sonic booms — were more extreme than typical urban sounds, and they changed each night, preventing full acclimation.
The lab environment itself, unfamiliar to participants, could have influenced results, as first-time sleepers in such settings often experience heightened alertness or discomfort. Despite these caveats, the findings add to a growing body of evidence questioning the unproven claims surrounding sleep aids. Pink noise machines have surged in popularity amid rising sleep anxiety, especially post-pandemic, with sales of white and colored noise devices climbing in recent years.
For those who swear by their noise machines, Basner advised moderation. "If a sound machine improves your sleep, play it at a low volume, and set a timer so it's not playing through the night," he recommended. "I don’t want to discount that there must be something behind it, because so many people are using it." This pragmatic approach acknowledges individual variability in sleep responses.
Beyond pink noise, the study underscores broader challenges in achieving restorative sleep in a noisy world. Urban dwellers, airport neighbors, and shift workers face constant auditory assaults that fragment sleep architecture. The American Academy of Sleep Medicine recommends seven to nine hours of quality sleep nightly for adults, yet surveys indicate over a third of Americans fall short, often citing noise as a factor.
Looking ahead, Basner and his team plan to expand the research, potentially including larger groups, longer durations, and diverse populations like children or older adults. They also aim to explore other colored noises, such as brown or green, which vary in frequency emphasis. Meanwhile, sleep experts urge consulting professionals before relying on gadgets, emphasizing proven strategies like consistent bedtimes and dark, quiet rooms.
As awareness of sleep science grows, this study serves as a reminder that not all interventions are benign. While pink noise may offer short-term comfort for some, its subtle erosion of REM could contribute to daytime fatigue, impaired focus, and emotional instability over time. For the millions turning to soundscapes for solace, the message is clear: listen closely to your body's signals, and perhaps consider the silence.