The wellness industry has been selling pink noise machines and apps as sleep aids for years, promising deeper, more restorative rest. A new study from Penn Medicine suggests they've been selling the opposite.

Researchers found that pink noise—that soft, steady whoosh marketed as a sleep enhancer—may actually reduce restorative REM sleep and interfere with sleep recovery. Meanwhile, the humble earplug significantly outperformed ambient sound machines at protecting sleep against traffic noise.

The findings challenge a multi-million dollar industry built on the premise that adding sound helps you sleep better. As it turns out, blocking sound might be the better strategy.

Pink noise is similar to white noise but with more emphasis on lower frequencies, creating a sound like steady rainfall or rustling leaves. It's been aggressively marketed as superior to white noise, with claims that it enhances deep sleep and improves memory consolidation. Sleep apps featuring pink noise generators have millions of downloads.

But the Penn Medicine study measured what actually happens to sleep architecture when people use these devices. REM sleep—the stage associated with dreaming, memory processing, and emotional regulation—took a hit. That's not a minor detail. REM sleep is when your brain does essential maintenance work. Disrupting it has consequences for mood, learning, and cognitive function.

The comparison with earplugs is particularly damning. When protecting against environmental noise like traffic, earplugs were "significantly more effective" at maintaining sleep quality. Simple, cheap, effective. No batteries required.

Now, to be clear about the science: this doesn't mean pink noise is harmful for everyone in every context. Sleep research is notoriously complex because sleep itself is complex—affected by stress, circadian rhythms, sleep disorders, environmental factors, and individual variation. What works for one person might not work for another.

But the burden of proof should rest with the people selling pink noise machines. If you're marketing a product as a sleep aid, it should demonstrably aid sleep. This study suggests that for many people, it might do the opposite.

The wellness industry has a long history of running ahead of the science—or ignoring it entirely. Pink noise machines became popular based more on marketing than on rigorous clinical trials. They sound scientifically plausible (frequency spectrums! brainwave entrainment!), which is often enough in the wellness market.