Sound machines that are intended to lull infants to sleep may be hazardous to their hearing. The white noise machines are popular shower gifts and registry items, but a recent study found that some of the machines exceeded workplace noise safety limits.
The study, from the University of Toronto, evaluated sleep machines. Looking at 14 popular models, the study found that at maximum volume the machines produced 68.8 to 92.9 decibels at a distance of 30 centimeters (about one foot). Three machines exceeded 85 decibels, which the National Institute for Occupational Safety and Health has determined is the workplace safety limit for adults on an eight-hour shift. The volume on one machine was so loud that with only two hours of use, workplace noise limits would be exceeded. Hospital nurseries have set noise limits at 50 decibels which all the machines tested exceeded at a distance of 100 cm.
Dr. Blake Papsin, senior author of the paper and chief otolaryngologist at Toronto’s Hospital for Sick Children says the machines are capable of delivering noise that may be unsafe for full-grown adults who work in mines.
Non-hazardous use of infant sound machines is possible while protecting infant hearing according to the study authors. Papsin and study colleagues suggest placing the machines as far away from the infants as possible, setting the volume as low as possible, and limiting the amount of time they are used.
In addition to fears for hearing hazards, another concern raised in the study is whether white noise can be harmful to auditory development. In 2003 the Journal of Science published a study that found that development of the brain’s hearing center in newborn rats was delayed by nonstop white noise . Infants may need to hear household sounds to develop. They may not be able to learn about the sounds in their environments if they are constantly masked by white noise.
According to Alison Grimes, head of audiology and newborn hearing at the University of California, Los Angeles Medical Center, Infants do their environmental learning by hearing speech and environmental sounds.
Papsin suggested that, theoretically, complex sounds, such as Mozart, would be best, while less complex sounds, such as white noise, would be worst.
Some sound machines are soft, plush animals, some designed to be attached to the crib. Sounds include ocean waves, babbling brooks, heartbeats, womb noises, or rainfall that are intended to mask household noise and allows the infant to sleep undisturbed. But there is also debate as to whether or not the machines actually help an infant sleep. Dr. Merrill Wise, pediatric sleep specialist and neurologist with the Methodist Sleep Center days that there is anecdotal evidence, but she is not aware of any study that scientifically looks at whether or not the machines actually help an infant sleep.
The study only looked at the sleep machines on maximum volume, not necessarily how parents of infants may actually use them. But it issues policy recommendations for less hazardous use, including requiring manufacturers to including a timer that would automatically turn off the the sound machines after a set period of time, limiting the maximum output level, and printing warnings on packages about the hazards of noise-induced infant hearing loss.
By Beth A. Balen