Drs. Sarah C. Hugh and Nikolaus E. Wolter of the University of Toronto; and Dr. Evan J. Propst, Karen A. Gordon, Dr. Sharon L. Cushing and Blake C. Papsin, all of the Hospital for Sick Children in Toronto and the University of Toronto, said infant sleep machines produce ambient noise or noise to mask other sounds in an infant's room as a means of increasing uninterrupted sleep.
The researchers tested 14 infant sleep machines at three distances: about 12 inches to simulate placement on a crib rail, 40 inches simulating placement near a crib and 80 inches to simulate placement across the room.
Three machines produced output levels of more than 85 dBA -- the noise of busy city traffic -- which, if played at these levels for more than 8 hours, exceeds current occupational limits for accumulated noise exposure in adults and risks noise-induced hearing loss, the study said.
Sounds that are 85 dBA or above can permanently damage adults ears. The more sound pressure a sound has, the less time it takes to cause damage -- for example, a sound at 85 dBA might take as long at 8 hours to cause permanent damage while a sound at 100 dBA could start damaging ear cells after only 30 minutes.
"The findings also determined that regular exposure to white noise through an infant sleep machine on a nightly basis can affect hearing, speech and language development," the study authors wrote.
"Even though the maximum output levels were measured in this study, the study authors encouraged parents to move infant sleep machines farther away than 80 inches and to lower the volume to protect infants' hearing."