Listening to pink noise, commonly used in sound machines and apps marketed as sleep aids, was associated with a decrease in restorative REM sleep and worse overall sleep recovery than wearing earplugs, a new study showed.

Results of a small clinical trial showed that people exposed to continuous pink noise reduced REM sleep by nearly 20 minutes, while using earplugs actually restored deep sleep typically disrupted by environmental noise.

“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 investigator Mathias Basner, MD, PhD, professor in the Division of Sleep and Chronobiology, Department of Psychiatry, University of Pennsylvania, Philadelphia, said in a news release.

The study was published online on February 2 in Sleep.

Deep Sleep, REM, and the Colors of Noise

Sleep cycles occur in multiple stages, including deep sleep and REM sleep. Deep sleep supports physical recovery, memory consolidation, and clearing of neurotoxins, while REM sleep aids emotional regulation, motor skill learning, and neurodevelopment.

Disruption of either stage has been associated with cognitive impairment, mood disorders, and neurodegenerative diseases, such as Parkinson’s disease. 

Since younger populations, including newborns and toddlers, spend a disproportionate amount of their sleep cycle in REM, disturbances in this stage may have neurologic consequences, impacting learning, memory, and emotional regulation, researchers wrote.

Broadband noise, such as pink, white, and brown noise, is widely used in ambient sound machines and sleep aid apps. White noise spreads sound evenly across all frequencies, producing a static-like sound. Pink noise emphasizes lower frequencies to produce a softer sound, such as the sound of rain, wind, or ocean waves. Brown noise boosts the lowest frequencies to create a deep, rumbling sound such as thunder.

Despite their popularity, evidence supporting the safety and efficacy of these sleep aids remains limited. Prior research has demonstrated that intermittent environmental noise, such as aircraft or traffic, can reduce deep sleep.

However, whether continuous broadband noise affects REM sleep architecture had remained unclear prior to this study.

The Sleep Test

The investigators conducted a randomized, controlled, crossover, polysomnographic sleep laboratory study at the Chronobiology and Isolation Laboratory in the Hospital of the University of Pennsylvania between November 2023 and June 2024.

A total of 25 healthy adults aged 21-41 years were enrolled, including 13 women and 12 men. The cohort included approximately 60% White, 24% Black, 12% Asian, and 4% participants from other racial backgrounds. Participants reported no history of sleep disorders, hearing impairment, or prior use of noise sleep aids.

Participants completed seven consecutive overnight laboratory sessions, each with an 8-hour sleep opportunity. During different nights, participants were exposed to four experimental conditions: environmental aircraft noise alone, continuous pink noise at 50 dBA, combined environmental noise plus pink noise, and environmental noise combined with earplug use. Participants wore earplugs throughout the 8-hour sleep session during the environmental noise plus earplug condition.

Environmental aircraft noise was delivered intermittently at varying sound pressure levels designed to mimic real-world nighttime aircraft exposure (approximately 50-60 dBA). Pink noise was delivered continuously at 50 dBA, roughly equivalent to moderate rainfall.

It was not possible to fully blind participants because they could perceive acoustic conditions, which investigators acknowledged as an inherent limitation of acoustic sleep studies.

To assess the primary outcome, sleep architecture, the investigators used full polysomnography, including electroencephalography, electrooculography, and electromyography sensors worn overnight.

They used standardized sleep scoring criteria from the American Academy of Sleep Medicine to measure time spent in deep sleep, REM sleep, periods of wakefulness after falling asleep, and overall sleep fragmentation.

Secondary outcomes included subjective sleep quality, mood, alertness, and neurobehavioral performance measured each morning.

What the Numbers Show

Aircraft noise alone reduced deep sleep by 23.4 minutes per night, compared with noise-free control nights. The use of earplugs restored16.9 minutes of deep sleep loss due to environmental noise, which represents a 72% recovery of noise-related reduction in deep sleep. 

Post hoc contrast analyses showed no statistically significant differences in measured sleep structure, mood, or alertness between earplug nights and control nights.

Pink noise alone reduced REM sleep by approximately 19 minutes compared with control conditions, but it did not significantly alter deep sleep. When combined, pink noise and aircraft noise shortened both deep and REM sleep significantly (P <.01) and increased time awake by 15 minutes.

Participants also reported lighter, more fragmented sleep with increased awakenings during exposure to pink or aircraft noise.

The findings suggest that continuous broadband noise may disrupt REM sleep, whereas earplugs may provide physiologic sleep protection without altering normal sleep architecture.

However, interpretation of the study’s findings is limited by its small sample size and controlled laboratory setting. The inability to blind participants to sound exposure may also affect generalizability and potentially introduce reporting bias.

Sleep Aid Caution

Among commonly used nonpharmacologic sleep aids, earplugs may offer greater protection of sleep architecture than pink noise, based on this study.

“… earplugs emerged as clearly superior in their efficacy to mitigate negative effects of intermittent EN [environmental noise] on sleep in comparison with constant PN [pink noise] exposure,” the investigators wrote.

They noted that broadband sounds are widely encountered in everyday environments, including household appliances such as fans and air conditioners. The investigators emphasized that more research is needed to determine safe acoustic exposure thresholds and optimal sound profiles for sleep.

“Future studies are needed to identify optimal noise color and level of broadband sounds before investigating effects of long-term exposure in the field,” they wrote.

Although sound machines are widely marketed as sleep aids, continuous broadband noise may unintentionally disrupt sleep stages that are most critical for neurodevelopment.

The investigators concluded, “While it is not clear how the findings of this study generalize to younger populations and chronic exposure scenarios, they caution against the use of BN [broadband noise] in newborns and toddlers until confirmatory studies are completed.”