Marketed as a pathway to deeper sleep, the gentle hum of pink noise has become a nightly ritual for millions. However, a recent University of Pennsylvania study suggests its use may reach at a cost to sleep quality.
Published last week in the medical journal Sleep, the study found that exposure to pink noise at night reduced REM (Rapid Eye Movement) sleep – the stage crucial for vivid dreams, memory consolidation, emotional regulation and learning. Researchers assessed 25 healthy adults over seven consecutive days in a controlled sleep lab environment.
“The negative consequences of the pink noise far outweigh the positive ones that we saw,” said Mathias Basner, a Penn professor of psychiatry and the study’s lead author.
Pink noise falls into a category known as “broadband noise,” characterized by a wide range of frequencies. White noise, often described as the auditory equivalent of white light containing all colors, is the most recognized example. Pink, brown, and other “colored” noises differ based on which frequencies they emphasize. Pink noise boosts lower frequencies, creating a sound akin to steady rainfall or ocean waves. While initially marketed for sleep, it’s also been promoted for improving focus and masking tinnitus.
These types of background noise are often used to mask unwanted sounds, a growing appeal in an increasingly noisy world. Since the release of the first white noise machine in the 1960s, hundreds of variations have emerged. Today, 10-hour videos of pink noise, often favored over white noise for its softer quality, garner millions of views on YouTube.
“So many people are using it, and it’s really indiscriminate use,” Basner observed.
Basner’s interest in the effects of noise on sleep began several years ago when he learned some individuals were using broadband noise as a sleep aid. This prompted a review of existing research, which he found largely inadequate. “We don’t know whether it’s working, whether it’s harmful or not,” he said.
To address this gap, Basner designed a study conducted in the highly controlled environment of a sleep lab at the Hospital of the University of Pennsylvania. Participants were monitored using polysomnography, a comprehensive test measuring brain waves, eye movements, and muscle tone. This allowed researchers to accurately identify sleep stages and assess biological responses to various conditions: no noise, environmental noise, pink noise, a combination of pink and environmental noise, or environmental noise with earplugs.
Over eight-hour sleep windows (lights out at 11 p.m., lights on at 7 a.m.), the team found that environmental noise – ranging from helicopter sounds to sonic booms – resulted in a 23.4-minute reduction in stage 3 sleep. This “deep sleep” phase is vital for physical recovery, immune function, and memory.
While pink noise didn’t impact deep sleep, it was associated with an average decrease of 18.6 minutes in REM sleep. “REM sleep is extremely important for a lot of things like memory consolidation, emotion regulation, brain plasticity, and neurodevelopment,” Basner explained.
He cautioned against the use of broadband noise machines in newborns, noting that infants spend approximately half of their sleep time in REM sleep, compared to a quarter for adults.
For adults who choose to use noise, Basner recommends using the lowest possible volume and setting a timer to automatically turn it off. However, he suggests foam earplugs as the most effective option. When used in conjunction with environmental noise during the study, earplugs recovered 72% of the lost deep sleep time, even though their effectiveness diminished at higher noise levels (around 65 decibels).
“You didn’t get the REM sleep reduction since they didn’t play anything back,” Basner said.
The study acknowledges limitations, including a relatively small sample size of younger, healthy individuals without pre-existing sleep disorders or hearing loss. The research also focused on short-term effects and was conducted in a lab setting, differing from real-world home environments. Basner intends to investigate the long-term effects of pink noise on sleep and explore other types of broadband noise.
“We necessitate to do the proper research to make sure that it is actually, at least, not harmful,” he said.
