Pink noise is often used to help people fall asleep, but new research suggests that it may interfere with the most restorative stages of sleep. A study by the Perelman School of Medicine at the University of Pennsylvania, published in the journal Sleep, found that pink noise reduced REM sleep and disrupted overall recovery during sleep. In contrast, wearing earplugs proved to be far more effective at protecting sleep from traffic noise.

These findings call into question the growing popularity of sound machines and sleep apps that rely on continuous background noise to promote rest. “REM sleep is important for memory consolidation, emotion regulation, and brain development. Our findings therefore suggest that playing pink noise and other types of broadband noise during sleep may be harmful—especially for children, whose brains are still developing and who spend much more time in REM sleep than adults,” said the study’s lead author, Mathias Basner, MD, PhD, professor of sleep and chronobiology in psychiatry.

Why Deep Sleep and REM Sleep are Important

The research team observed 25 healthy adults between the ages of 21 and 41 in a controlled sleep laboratory. Participants were given eight hours of sleep for seven nights. None of them reported suffering from sleep disorders or regularly using noise to help them fall asleep.

During the study, participants slept under different conditions. These included exposure to aircraft noise, pink noise alone, a combination of aircraft noise and pink noise, and aircraft noise with earplugs. Each morning, participants completed cognitive tests and questionnaires to assess sleep quality, alertness, and other health-related effects.

During a typical night, the brain repeatedly cycles through periods of deep sleep and REM sleep. Deep sleep plays an important role in physical recovery, memory processing, and the removal of waste products from the brain. REM sleep, often referred to as dream sleep, supports emotion regulation, motor skill development, and brain growth. Together, these sleep stages provide balance so that people wake up refreshed and mentally ready for the day ahead.

What is Pink Noise?

Pink noise belongs to a category known as broadband noise. It is a continuous sound that covers a wide frequency range and has a uniform, static-like quality. It is a special form of so-called broadband noise, i.e., a continuous noise that contains many or even all audible frequencies simultaneously. The key difference from other types of noise is how the energy is distributed across these frequencies. With pink noise, the energy decreases as the frequency increases: low tones are more prominent than high tones. This makes pink noise sound more balanced, softer, and less “hissing” to the human ear than white noise, for example, where all frequencies are equally strong.

This distribution fits surprisingly well with the way our hearing works. We naturally perceive low frequencies more strongly than high ones, which is why pink noise is often perceived as more pleasant and natural. Many sounds from the environment resemble this pattern, for example, steady rain, wind in trees, the sound of the sea, or even the distant sound of a waterfall. Everyday technical noises such as fans, air conditioning systems, or a steadily running motor also often tend toward pink noise.

Due to these characteristics, pink noise is often used specifically to promote concentration, mask disturbing background noise, or as a sleep aid. It also plays an important role in acoustics and sound engineering, for example when testing loudspeakers or rooms, as it comes closer to the natural hearing experience than other types of noise. Overall, it can be said that pink noise is a kind of “natural-sounding noise” that bridges the gap between technical definition and everyday listening experience.

Each type of noise distributes sound energy differently across the audible spectrum, which affects whether it sounds higher or lower. Many natural sounds, including rain and ocean waves, fall into this category. Common household appliances such as fans and air conditioners also produce broadband noise. Broadband noise also includes white noise and other variants such as brown and blue noise.

Key Findings of the Study

Compared to nights without noise, exposure to aircraft noise resulted in an average loss of about 23 minutes per night of “N3” sleep, the deepest stage of sleep.Wearing earplugs largely prevented this loss of deep sleep. Pink noise alone, played at 50 decibels (often compared to the sound of “moderate rain”), was associated with a reduction in REM sleep of almost 19 minutes. When pink noise was combined with aircraft noise, the effects were even more pronounced.

Both deep sleep and REM sleep were significantly shorter, and participants spent an additional 15 minutes awake during the night. This increase in wakefulness was not observed when participants were exposed to aircraft noise or pink noise alone. Participants also reported that their sleep felt lighter, they woke up more often, and their overall sleep quality deteriorated when exposed to aircraft noise or pink noise. These negative effects were largely absent when earplugs were used.

What this Means for Millions of Sleepers

The researchers said the findings confirm the effectiveness of earplugs, which many people use to help them sleep better. At the same time, the findings underscore the need for more thorough investigation of the long-term health effects of pink noise and other broadband noises marketed as sleep aids.

Millions of people rely on continuous background noise every night. White noise and ambient podcasts alone account for three million hours of listening time on Spotify every day, and the five most popular YouTube videos for the search term “white noise” have a combined total of more than 700 million views. Despite this widespread use, studies examining how broadband noise affects sleep remain limited and often inconclusive, according to a recent review by Basner and colleagues.

REM sleep disruption is common in conditions such as depression, anxiety, and Parkinson’s disease. Basner also pointed out that children spend significantly more time in REM sleep than adults, which may make them particularly sensitive to its disruption. Nevertheless, many parents place sound machines near the beds of newborns and young children to help them fall asleep and stay asleep.

“Overall, our findings caution against the use of broadband noise, especially in newborns and infants, and indicate that we need more research on vulnerable populations, long-term use, the different colors of broadband noise, and safe broadband noise levels in relation to sleep,” Basner said.