If you’re one of the millions of people who use a white noise machine at night, there’s a good chance it doesn’t actually produce true white noise. Instead, many of these sleep aids produce pink noise, a broadband sound that filters out the higher frequencies many people find annoying or distracting. Pink noise, previous studies have shown, can deepen sleep, but research published today in the journal Sleep suggests it might not be all it’s cracked up to be.
To study the effect of pink noise on sleep, researchers from the University of Pennsylvania School of Medicine monitored 25 adults in a sleep laboratory for seven nights, exposing them to aircraft noise, pink noise, or both. In the morning, participants completed surveys detailing the previous night’s quality of sleep.
They found that exposure to aircraft noise shortened the amount of time spent in the deepest stage of sleep by about 23 minutes, while exposure to pink noise shortened the amount of time spent in REM sleep by 19 minutes. When aircraft noise and pink noise were played, both stages of sleep were significantly shortened, and time spent awake was 15 minutes longer. Understandably, participants reported that their overall sleep quality suffered during nights with noise compared to noise-free nights.
Read more: “Noise Is a Drug and New York Is Full of Addicts”
“REM sleep is important for memory consolidation, emotional regulation, and brain development, so our findings suggest that playing pink noise and other types of broadband noise during sleep could be harmful—especially for children whose brains are still developing and who spend much more time in REM sleep than adults,” study author Mathias Basner explained in a statement.
It seems like bleak news for the millions of people who cue up a pink noise playlist at night, but the researchers stress that more study is needed on other broadband noise spectrums.
“Overall, our results caution against the use of broadband noise, especially for newborns and toddlers, and indicate that we need more research in vulnerable populations, on long-term use, on the different colors of broadband noise, and on safe broadband noise levels in relation to sleep,” Basner said.
It’s not all bad news, though. The research team did find one lo-fi sleep aid for restless sleepers bothered by traffic noise: earplugs. Participants who wore them while being exposed to aircraft noise showed sleep patterns similar to noise-free nights. 
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