White noise machines are not necessarily as benign as it may seem for sleep health, reports Bustle.

For starters, “consistently falling asleep to the sound of a white noise machine will create a sleep association,” Dr. Sujay Kansagra, a sleep expert with Mattress Firm, tells Bustle. “That means over time your brain will associate the process of going to sleep with having the white noise machine on. This makes it more difficult to fall asleep without the sound of one, and leads people to believe they need to hear that sound to sleep.”

“Research on the effect of white noise on the brain is minimal and conflicting, but some studies show that ongoing ambient noise can cause the brain to react the same way it would to stress,” Rose MacDowell, a sleep expert and chief research officer at Sleepopolis, tells Bustle. “This can result in release of the ‘stress hormone’ cortisol, and decreased levels of dopamine in parts of the brain that control learning and memory.”