Pink noise, a staticky sound that’s supposed to help people fall asleep, may actually worsen your rest, a new study found.
Pink noise — like white noise — contains all the frequencies humans can hear, but it plays lower frequencies more prominently. Sounds that are used for different types of brain stimulation or relaxation are assigned a color based on how their noise spectrum matches with a colored light spectrum. White noise plays all frequencies at the same intensity, and white light combines all the visible light colors.
Pink noise has been compared to sounds of rain and ocean waves. Research on its benefits for memory and sleep has been mixed.
University of Pennsylvania researchers conducted a seven-night sleep lab study involving 25 healthy adults, mostly younger women, to determine the effects of environmental noise, pink noise and earplugs on sleep quality. None of the participants had sleep disorders or regularly used ambient sound machines.
Lights were out at 11 p.m. each night and participants were awakened at 7 a.m.
During the sleep period, participants were exposed to either: no noise, environmental noise only, pink noise only, a combination of the pink and environmental noise at varying decibels, and environmental noise only with earplugs.
The environmental noise ranged from traffic sounds to sonic booms.
When sleeping, the brain cycles through different stages, including light, deep and rapid eye movement, or REM. REM sleep is when dreaming occurs.
The study, published Monday in the journal Sleep, found environmental noise mainly disrupted Stage 3 sleep, reducing it by 23.4 minutes on average. Stage 3 is the deepest sleep state and is important for cognitive function and memory.
The study also found that pink noise reduced the time spent in REM sleep by 18.6 minutes, a crucial sleep stage for mood regulation and mental focus.
Dr. Mathias Basner, professor of psychiatry at the University of Pennsylvania Perelman School of Medicine and the study’s lead author, said he didn’t expect pink noise to disturb sleep to that degree.
“There have been studies that have reported the REM sleep reduction already,” he said. “Research has been there, but it has been neglected, and we kind of uncovered that again.”
Before and after each night, researchers conducted physiological and cognitive tests to determine how the noises affected participants. Participants were also monitored during their sleep and were surveyed on their mood and fatigue.
Losing 20 minutes of REM sleep may not seem like a lot, but Basner said the minutes can stack up.
“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 said.
The study didn’t observe the effects of ambient noise on babies or children. REM sleep loss may be more pronounced for newborns, Basner added, which makes up half of their sleep compared with only 25% in adults. He cautioned against the use of noise machines for infants and toddlers.
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,’” he said.
It’s unclear why the pink noise disturbed the REM phase, although “constant auditory input” could inhibit brain processes responsible for sleep, Basner said.
Pink noise did help participants sleep through traffic sounds, but earplugs were more useful for blocking it out.
The study has several limitations. The sample size of 25 adults is small, and they were observed only for seven nights, a short time period. It’s possible that over a longer period of time participants could adjust to pink noise and their sleep would return to normal. Similarly, the environmental noise consisted of jets, helicopters, sonic booms and other noises that are not typical — noises that people could also become accustomed to over time.
The noises also changed each night, meaning participants consistently slept under different conditions. The study was conducted in a lab, where participants had never slept before, which could have also disturbed their sleep.
Dr. Rafael Pelayo, clinical professor in the division of sleep medicine at Stanford University School of Medicine, said because participants were in a lab, the findings might not apply to the average person at home.
“The need for sleep is biological, but the way we sleep is learned,” he said, meaning people can adjust to any condition like a snoring partner.
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, Basner said.
“I don’t want to discount that there must be something behind it, because so many people are using it,” he said.
