"Pink noise” has become a trendy sleep aid, but a new study says it actually might interfere with brain activity during sleep.

People listening to pink noise suffered a decrease in the amount of time they were in REM sleep, the stage of sleep in which dreams occur, researchers reported Feb. 2 in the journal Sleep.

“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,” lead researcher Dr. Mathias Basner said in a news release. He’s a professor of sleep and chronobiology in psychiatry at the University of Pennsylvania.

On the other hand, earplugs effectively blocked traffic noise and protected people’s sleep without affecting their sleep cycles, researchers found.

These results challenge the widespread use of ambient sound machines and sleep apps, both of which feature pink noise, researchers said.

“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.

When humans sleep, they cycle multiple times through periods of deep sleep and REM sleep, when most dreaming occurs. (REM is shorthand for rapid eye movement.)

Deep sleep is important for physical restoration and clearing toxins from the brain, researchers said in background notes. 

On the other hand, REM sleep is important for cognitive matters like storing memories and regulating emotions.

In this way, deep and REM sleep complement each other and help people wake up restored both in body and mind, researchers said.

For the new study, researchers observed 25 healthy adults ages 21 to 41 in a sleep laboratory over seven consecutive nights. All participants hadn’t used noise to help them sleep, and reported no sleep disorders.

The participants slept under different conditions, including exposure to aircraft noise and/or pink noise, as well as wearing earplugs to block noise.

Pink noise is a continuous sound spread across a wide range of frequencies. It sounds much like the static heard when you dial to an empty broadcast channel on TV.

Researchers found that pink noise at 50 decibels — about the level of moderate rainfall — was linked to a nearly 19-minute decrease in REM sleep.

Likewise, exposure to aircraft noise reduced nightly deep sleep by about 23 minutes, results showed.

Pink noise combined with aircraft noise interfered with both deep and REM sleep, and time awake was about 15 minutes longer, researchers found.

Participants also reported that their sleep felt lighter, they woke up more frequently, and had worse overall sleep when exposed to either pink noise or aircraft noise.

However, the effects of either type of noise went away when people wore earplugs.

Researchers noted that REM sleep disruption is a common feature of disorders like depression, anxiety and Parkinson’s disease.

Children spend a lot more time in REM sleep, and thus might be particularly vulnerable to the negative effects of pink noise, researchers said.

“Based on these findings, it is likely warranted to discourage the popular use of broadband sounds in newborns and toddlers, as REM sleep plays a critical role in neurodevelopment in these age groups, although further confirmatory studies are needed,” the research team concluded in their paper.