If you bought a "sleep machine" that makes soothing sounds in an effort to help your baby slumber, be careful: At top volume, such machines can actually hurt infants' hearing, researchers say. Sleep machines, which often emit nature sounds or white noise and sometimes come inside stuffed animals, are often recommended by sleep experts. But researchers tested out 14 of the most popular models and found that at top volume they produced anywhere from 68.8 to 92.9 decibels when placed 30 centimeters from an infant's head—the workplace safety limit for adults on an eight-hour shift is 85 decibels, and three of them exceeded that, the New York Times reports. (Thirty centimeters is about the distance from a baby's head to the crib rail, CNN notes.)
And at 100 centimeters away, all of them were louder than the 50-decibel limit set by hospital nurseries—in fact, all but one were still louder than that limit even when placed 200 centimeters away, the equivalent of across the room, USA Today reports. "These machines are capable of delivering noise that we think is unsafe for full-grown adults in mines," says the lead researcher. "Exposure to these devices may place infants at risk of developing noise-induced hearing loss or maldevelopment of the auditory system," the study says, according to ABC News. But experts say the machines can be used safely, as long as they are placed farther away from babies, used at a lower volume, or used for less time.