For those in search of safe, non-drug sleep aids, sound machines are a popular choice. A National Sleep Foundation poll from 2012 found that 5% of Americans sleep with a “sound conditioner,” which is a catchall term for a fan, phone app, or other noise-producing device.
Michael Grandner, director of the Sleep and Health Research Program at the University of Arizona, says the “blanket of sound” these create is a lifesaver if you live on a busy street or anywhere else where loud nighttime noise is common. But even if your bedroom is pin-drop quiet, sound machines can be helpful, if you’re the type of person unsettled by a total absence of noise, or if you’re a light sleeper who wakes from even the softest sound.
Research supports the idea that a little background sound can help people tune out sleep-disrupting creaks or clatter. For a small 2005 study in the journal Sleep Medicine, researchers exposed sleepers to recorded hospital sounds either with or without a white noise machine. Their analysis of the sleepers’ brain waves found that those who slept with the white noise machine were hardly disturbed by the hospital sounds, while sleep arousals were frequent among those who slept without white noise.
There’s also so-called “pink noise” and “brown noise,” which can sound similar to white noise, but have different underlying acoustical properties. While white noise is composed of a more or less equal mix of low-, medium-, and high-frequency sounds, pink noise and brown noise emphasize low-frequency tones to a greater degree. Grandner describes pink noise as a hiss while brown noise is more of a shush. White noise falls somewhere in between, he says.
A 2012 study in the Journal of Theoretical Biology found people enjoyed more stable, high-quality sleep when exposed to pink noise, as opposed to silence. Also, a 2017 study from Northwestern University found “sleep-dependent memory” scores improved among older adults after they slept with pink noise humming in their ears. There’s not much sleep research on brown noise, but Grandner says this is the one he prefers himself.
While companies that produce and market these noise machines—whether they make pink noise, brown noise, white noise, or other sounds—make a big deal of these sorts of findings, experts say all of this research is preliminary. “A more definitive study would be quite expensive and nobody has been willing to fund one,” Grandner says.
“I don’t think there’s enough evidence yet to say one type is better than another,” says Michelle Drerup, a sleep psychologist at the Cleveland Clinic. She’s unaware of any research that directly compares pink noise to white noise in terms of their effects on sleep. “I know from talking with my patients that some people prefer natural sounds, like a rainstorm or the rush of water, whereas others don’t want a sound they can attach an image to,” she says. Still others find all of these noises aggravating, she adds.
Based on the existing research, the optimal type of sound for sleep comes down to personal preference. “It all depends on the individual,” Grandner says
For some, the optimal sound might be none. “Biologically, you don’t need this [sound] to sleep,” he says, “and if you use it every night, you can get so used to it that you can’t sleep without it.” He likens these sound machines to both a “crutch” and a form of psychological addiction—albeit a relatively harmless one. The benefits of a sound machine can outweigh this downside, he says. But if background noise or silence isn’t the source of your sleeping issues, you may want to think twice before you add a sound machine to your bedtime routine.
Other sleep experts agree. “I wouldn’t recommend [sound machines or apps] to someone unless they’re reporting difficulties with outside noises, or some type of environmental disrupter,” Drerup says. “Some people develop these rituals where they think they need to have something or they can’t sleep, or they get anxious when it’s not there, and that includes [sound machines].”
One thing Grandner advises for anyone and everyone: don’t sleep with a television on. “That’s too much variability,” he says of the sounds TVs emit. Whether a noise-sensitive sleeper prefers a fan, a sound machine, or a sounds-of-nature app, the important thing is that the ambient sound is predictable and consistent.