Sound machines have become a standard item on baby registries, with settings for white noise or babbling brooks meant to lull infants and toddlers into a state of deep sleep -- and keep them that way.
But a new study suggests the machines could be harmful, capable of producing sound pressure levels that could potentially harm babies' auditory development. Its researchers are calling for manufacturers to print warnings about noise-induced hearing loss on packaging and urging parents to exercise caution.
"At maximum volume, three of [the machines] exceeded the safe levels for adult occupational noise," Dr. Blake Papsin, director of the Cochlear Implant Program at The Hospital for Sick Children in Canada and a researcher on the study, told The Huffington Post. "Maybe they're not so good for the baby. Maybe they don't want to hear a heart sound. Maybe they want to hear their environment."
Papsin and his colleagues measured the maximum sound outputs of 14 machines that are widely available throughout the United States and Canada. They analyzed sound levels at three distances: 30 centimeters away (meant to mimic placement on a crib rail); 100 centimeters (near a crib) and 200 centimeters (across a baby's room). The measurements were adjusted to account for the effect they might have on a 6-month-old's ear canal, which is smaller and shaped differently than an adult's.
Each one of the machines exceeded 50 dBA -- the recommended noise limit for infants in nurseries -- and all but one were capable of producing levels exceeding that limit even when measured at a distance of 200 centimeters.
"This is a very worrisome and concerning paper, and it's likely to lead to a re-examination of whether these devices are really in babies' best interest," said Dr. Merrill Wise, a pediatric sleep specialist and neurologist with the Methodist Sleep Center in Memphis, Tenn., and a board member at the American Academy of Sleep Medicine. He did not work on the study.
Before reviewing the new findings, Wise said he likely would have told any parents considering a sound machine that he had no strong opinion on the matter.
"From a sleep perspective, I'm not aware of any studies which have looked at whether they're effective at improving sleep," he said. "There is anecdotal evidence, but I'm not aware of any study that scientifically looks at this question."
But now, Wise said, he would be far more cautious.
"This paper has raised some very significant questions with regard to safety, and there is clearly a need for caution and for gathering more data," he said.
The authors of the new study acknowledge that a major limitation of their research is that it analyzed the machines' maximum output levels, but not necessarily how parents use them in everyday life. "Our concern, however, is that these devices are sold with limited or no instructions for safe use," the study says.
With that in mind, it issues policy recommendations for safer use.
Manufacturers should limit the maximum output level of their machines, and print warnings on packaging about noise-induced hearing loss. They should also be required to include a timer for any machines marketed toward infants that would automatically turn off the device after a set length of time, the researchers argued.
Parents, on the other hand, should place sound machines as far from their babies' cribs as possible, and never place them in a crib. Machines should be played at low volumes and kept on for short stretches only, Papsin said, adding that theoretically, complex sounds would be best (think Mozart) while the least complex (white noise) would be the worst.
"I'm not going to say don't use these ... but if you are going to, use it cautiously," he said. "Me personally? I wouldn't."