White, pink, brown, green—the wellness aisle now sells silence back to you by the colour. A counselling psychologist sorts the real evidence from the marketing.
Somewhere between the magnesium gummies and the blue-light glasses, the wellness aisle worked out that silence can be sold back to you in colours. White noise to fall asleep. Pink noise for deeper sleep. Brown noise for focus. Green noise for—and I had to read the packaging twice—a general sense that things are going to be alright. There are apps. There are eight-hour loops on YouTube. There is, inevitably, a subscription.
The sceptic’s question is the right one: is any of this real, or is it the audio equivalent of a homeopath charging you for expensively shaken water?
The honest answer is more interesting than either camp wants it to be. Some of it is real. Some of it is real but nothing like what’s on the label. And a fair chunk is a colour the marketing department invented on a Tuesday. Let me sort the four into their proper boxes.
The physics, at least, is not lying to you
The colours are genuine signal profiles, not vibes. White noise carries roughly equal power across every frequency the ear can register—the hiss of an untuned radio. Pink noise tips the balance towards the low end, dropping off as frequency climbs (the 1/f roll-off), which lands somewhere near steady rain. Brown noise tips further still, all rumble and waterfall, and takes its name not from the colour but from Robert Brown and the drunkard’s-walk mathematics of Brownian motion. Green noise we’ll come back to, because green noise is where the story quietly goes sideways.
So far, so respectable. The trouble starts the moment anyone bolts a health claim onto the hiss.
The boring true bit: masking works
Here is the least glamorous and most defensible thing noise does. It masks. A steady, broadband sound raises the floor of what the brain has to notice, so the slammed car door, the neighbour’s television, the 3am motorbike, and the dog with strong opinions about the moon no longer punch through the quiet and haul you awake. Reviewing the field, Riedy and colleagues put it plainly: these machines work by partially masking external sound and raising the threshold at which a noise will interrupt you (Riedy et al., 2021).
That’s the mechanism most people are actually buying, and it’s a perfectly good one. A cheap fan does the same job for the price of moving some air. You don’t need a colour for this. You need a sound that doesn’t change and doesn’t ask anything of you.
The sleep claims don’t survive contact with the evidence
Now the marketing. The promise isn’t “this masks your neighbour”; it’s “this improves your sleep.” And when you go looking for the studies to hold that promise up, the floor gives way.
Riedy et al. (2021) ran a systematic review of thirty-eight studies of continuous noise as a sleep aid. Under GRADE—the standard framework for rating how far a body of evidence can be trusted—the quality of the evidence that continuous noise improves sleep came out as very low. It didn’t land on “promising,” or even “mixed.” Very low, which in GRADE terms is a polite academic way of saying you should hold your enthusiasm with tongs.
Worse than merely underwhelming, there’s a plausible route to harm. Run the hiss loud enough, all night, every night, and you may be sanding down the very sleep you’re trying to protect, since high-intensity white noise has been linked with reduced REM and disturbed sleep architecture. And in the specific case of white-noise therapy for tinnitus, Attarha and colleagues documented what they called otolaryngology’s “cobra effect”—a fix that, over time, can worsen the very auditory processing it was meant to soothe (Attarha et al., 2018). The cobra effect, for the uninitiated, is the name economists give to a solution that breeds more of the problem it was hired to kill.
A second review, comparing white against pink against mixed audio, found pink noise had the better hit-rate on paper: positive sleep findings in most pink-noise trials, versus roughly a third of the white-noise ones. It still landed on the same sober conclusion, though, that there’s no strong evidence for any of it, even if a night or two does no measurable harm (Capezuti et al., 2022). File that under “might help, probably won’t hurt, don’t remortgage.”
The one genuinely interesting island, and how it’s mis-sold
Here is where it gets good, and where the wellness industry performs its neatest sleight of hand.
There is real, carefully-run research showing pink noise can deepen slow-wave sleep and sharpen memory. Papalambros and colleagues at Northwestern took healthy older adults, read their brain activity in real time, and delivered brief pulses of pink noise precisely timed to the upstate of each sleeper’s own slow oscillations. The payoff: larger slow waves, and better recall on a word test the next morning (Papalambros et al., 2017).
Read that method again, because the method is the whole game. The pink noise wasn’t playing all night. It arrived in fifty-millisecond pulses, fired by a phase-locked-loop algorithm reading the sleeper’s live EEG, aimed at a specific millisecond-wide window inside a specific brain rhythm. That’s less a sleep playlist and more a very patient engineer sitting inside your skull, tapping a tiny drum exactly on the beat.
What’s sold to you is an eight-hour mp3. What the study did is closed-loop, individually targeted neural stimulation in a lab. Citing the second to sell the first is like citing the moon landing to sell a trampoline. Both, technically, involve going up. They are not the same enterprise.
The island closest to home: noise and the AuDHD brain
This is the one I have skin in, so let me declare the interest. I’m a late-diagnosed AuDHD adult, and when I first landed in Đà Lạt I did my best writing at One More Café, wrapped in a cheerfully relentless playlist of Western songs any of us would recognise from the 70s through to now. Silence, back then, felt about as conducive to concentration as a job interview. I’d filed that under character flaw for years. It turns out it may be a dopamine curve.
The Moderate Brain Arousal model (Sikström & Söderlund, 2007) proposes that ADHD involves low tonic dopamine, and that a brain in that state needs more external stimulation, noise included, to reach the arousal level where it works properly. The mechanism they borrow is stochastic resonance: a real and well-attested phenomenon in which adding a little random noise to a weak signal can nudge it over the threshold of detection rather than burying it. Too little, and the signal never fires; too much, and it drowns; the right amount, and it lands.
The empirical hook arrived the same year. Söderlund, Sikström and Smart (2007) found that white noise improved cognitive performance in children with ADHD while degrading it in typically developing children: the same hiss, opposite effects, depending entirely on the brain receiving it. If you’ve ever been baffled that the background racket which helps you concentrate drives your partner up the wall, that asymmetry is the whole finding, compressed into one domestic argument.
Except the story refuses to sit still, which is the useful part. These days I’ve drifted up the hill to the open air and quiet of Rừng Thông Mơ Farm & Bistro, and the loud, familiar pop I once leaned on has been supplanted by—of all things—posh café jazz and 60s crooners leaking from tiny speakers bolted beside every table. Sinatra, uninvited, at a volume too low to enjoy and too present to ignore. And I don’t reach for more noise. I reach for over-ear noise-cancelling headphones and work inside the silence they manufacture. Same brain, opposite prescription, a few months apart.
That looks, at a glance, like the model falling over. Read the fine print and it doesn’t. Sikström and Söderlund’s own account has moderate, non-salient stimulation helping while strong or salient stimuli hijack attention outright—and little is more salient than half a crooned lyric you didn’t ask for, arriving at the wrong volume from the wrong direction. Loud pop I chose and knew by heart was arousal without ambush. Low crooners I didn’t choose are ambush without arousal. Dose isn’t the only variable; so is whether your brain keeps having to turn around to check what that new sound was.
I’ll leave the humility switch on, though, because both the evidence and my own voice insist on it. This is mostly children, mostly short lab tasks, and the underlying mechanism is now being poked at hard. A 2026 critical appraisal found that pink noise and a plain pure tone both reduced neural noise in adults with elevated ADHD traits, which isn’t quite what a clean stochastic-resonance story predicts and hints that the model may need rebuilding rather than merely reciting (Rijmen et al., 2026). The effect looks real. The explanation is still under construction. Both those things can be true at once, and pretending otherwise is how you end up selling trampolines to astronauts.
Green noise, or the colour of the marketing department
Which brings us, at last, to green.
White, pink and brown have agreed technical definitions you can write as equations. Green does not. Ask three sound engineers what green noise is and you’ll collect a mid-frequency hump, a shrug, a vague gesture towards “nature,” and a definition that mysteriously matches whatever the app store is selling this quarter. It’s usually described as white noise with the middle frequencies boosted, marketed as the sound of oceans and forests, and supported by approximately no dedicated research. It rose to prominence not through a journal but through social media, which is a fine place to find a recipe and a dreadful place to find a mechanism.
I’m not claiming green noise can’t relax you. Rain relaxes people, and a boosted mid-band that sounds like rain may well do the same. I’m claiming the colour is doing no work the sound wasn’t already doing, and that the specificity—green, rather than merely “pleasant hiss”—is a pricing strategy wearing a lab coat.
So, bullshit or not?
Here’s the verdict, sorted back into the four boxes we started with. Masking is real and boring, and a cheap fan delivers most of it. The overnight sleep-improvement claims rest on evidence rated very low, with a real possibility of harm if you run it loud and forever. The pink-noise-and-memory finding is genuine science that’s been quietly amputated from its method and stitched onto a product it never studied. And the noise-and-focus effect, the one that might explain why some of us think best inside a storm of sound, is the most promising of the lot for neurodivergent brains while still being early, mostly-in-children, and mid-argument about why it works.
The practical version, then. If a steady sound helps you sleep or focus, use it, keep the volume modest, and pay as little as you can for the privilege. If someone’s charging a premium for a specific colour and waving a lab study to justify it, keep one hand on your wallet. The hiss might be helping you. The story wrapped around the hiss is where the money hides.
Silence, it turns out, is neither golden nor for sale. But someone will always try to sell it to you by the litre, in colour, with a subscription.
References
Attarha, M., Bigelow, J., & Merzenich, M. M. (2018). Unintended consequences of white noise therapy for tinnitus—Otolaryngology’s cobra effect: A review. JAMA Otolaryngology–Head & Neck Surgery, 144(10), 938–943.
Capezuti, E., Pain, K., Alamag, E., Chen, X. Q., Philibert, V., & Krieger, A. C. (2022). Systematic review: Auditory stimulation and sleep. Journal of Clinical Sleep Medicine, 18(6), 1697–1709. https://doi.org/10.5664/jcsm.9860
Papalambros, N. A., Santostasi, G., Malkani, R. G., Braun, R., Weintraub, S., Paller, K. A., & Zee, P. C. (2017). Acoustic enhancement of sleep slow oscillations and concomitant memory improvement in older adults. Frontiers in Human Neuroscience, 11, 109. https://doi.org/10.3389/fnhum.2017.00109
Riedy, S. M., Smith, M. G., Rocha, S., & Basner, M. (2021). Noise as a sleep aid: A systematic review. Sleep Medicine Reviews, 55, 101385. https://doi.org/10.1016/j.smrv.2020.101385
Rijmen, J., Senoussi, M., & Wiersema, J. R. (2026). Pink noise and a pure tone both reduce 1/f neural noise in adults with elevated ADHD traits: A critical appraisal of the moderate brain arousal model. Journal of Attention Disorders. Advance online publication. https://doi.org/10.1177/10870547251357074
Sikström, S., & Söderlund, G. (2007). Stimulus-dependent dopamine release in attention-deficit/hyperactivity disorder. Psychological Review, 114(4), 1047–1075. https://doi.org/10.1037/0033-295X.114.4.1047
Söderlund, G., Sikström, S., & Smart, A. (2007). Listen to the noise: Noise is beneficial for cognitive performance in ADHD. Journal of Child Psychology and Psychiatry, 48(8), 840–847. https://doi.org/10.1111/j.1469-7610.2007.01749.x
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