The lulling white noise or gentle sounds of nature that an infant sleep machine (ISP) emits can bring relief to wakeful babies and their exhausted parents. However, research by scientists at the University of Toronto suggests that these popular devices, if not used carefully, can pose a threat to an infant’s hearing.
A study published online on March 3 in the journal Pediatrics concludes, “ISMs can generate sound levels in excess of adult occupational noise limits and more conservative limits created for infants in hospital nurseries. Exposure to these devices may place infants at risk of developing noise-induced hearing loss or maldevelopment of the auditory system.”
In their research, the scientists tested 14 different models of the sleep-inducing devices. Turning the ISMs up to their maximum volume, the researchers measured sound levels at various distances from the machines. They found that at 30 centimeters (11.3 inches) from the device, which is about the distance from a baby’s head that an ISM might be placed, the sound levels ranged from 68.8 to 92.9 dB.
Applying correction factors to account for the differences between a 6-month-old’s ear canal and that of an adult, the investigators found that all the machines produced greater than 50 A-weighted dB, which is the recommended noise limit for infants in hospital nurseries. Therefore, they advised, “We suggest that the consistent use of these devices raises concerns for increasing an infant’s risk of noise-induced hearing loss.”
The study also found that the sound from the three noisiest ISMs measured at a distance of 30 centimeters exceeded 85 dB, which is the maximum time-weighted average sound level over an 8-hour shift in the workplace permitted by NIOSH (National Institute for Occupational Safety and Health).
The message of the study, the authors say, is not that parents should entirely give up on using ISMs to help their baby and themselves sleep. They wrote, “The safe use of an ISM may be possible, but requires policy recommendations for manufacturers and recommendations for families that outline the parameters for their use.”
The authors offered some specific recommendations. Among them are that manufacturers be required to limit the maximum output of their ISMs and to place warnings on the packaging about possible risk to infants’ hearing. The reseachers also suggested requiring manufacturers to include a timer on all devices that would automatically shut it off after a predetermined period of time.
The researchers advised that parents who want to use an ISM be instructed to place it well away from their baby and never in the crib or on the crib rail. They should also play the device at a low volume and leave it on for only a short time.
In an interview with The New York Times, Blake C. Papsin, MD, the senior author of the paper, said that he got the idea for the study after an experience at the Hospital for Sick Children in Toronto, where he is chief otolaryngologist. The parent of a baby who was a patient in the hospital brought in a portable white noise machine, which Papsin described as sounding like the roar of water in a commercial carwash.
Not every expert on children’s hearing is convinced that the danger posed by ISMs to babies’ hearing is as great as the Toronto findings suggest.
Brian J. Fligor, ScD, director of diagnostic audiology at Children’s Hospital Boston and an instructor in the Department of Otology and Laryngology at Harvard Medical School, told the Times that the study may have overestimated the sound exposure to infants by roughly 7 dB because of how the authors accounted for the differences between the ear canals of adults and newborns. Fligor said, “I don’t see these results as a call for drastic reduction in use” of ISMs.