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Infant sleep machines designed to soothe baby with sound are popular with harried parents, but they could end up harming babies' hearing, according to a new study.
Researchers tested 14 widely available machines that play white noise and other soothing sounds for an article published Monday in the journal Pediatrics. At one foot away, three of the machines produced such intense sound levels at maximum volume that, if played through the night, they would exceed allowable noise limits for adults at work.
"Used too loud or too close or too long, these machines can exceed safety standards and potentially damage the hearing of the infant," Dr. Blake Papsin, the lead researcher and chief otolaryngologist at The Hospital for Sick Children in Toronto, told NBC News.
And those sound limits may be too liberal for infants, whose ears differ from adults', says Papsin. "The infant ear has a little straighter tube. It's a little wider open, and it amplifies the higher frequencies."
At distances of one foot and three feet, the maximum volume on all the devices exceeded the more conservative recommended noise limit for infants in hospital nurseries, and at 6 1/2 feet, 13 of the devices did so.
The study only looked at the potential for harm: No one knows how parents actually use these machines, and there have been no hearing studies of infants exposed to them.
But the researchers recommend that parents play the machines as quietly as possible, as far from the baby as possible, and for as short a time as possible. Or maybe not use them at all.
"None of our sleep specialists recommend them," says Papsin, who suggests that parents address underlying noise issues and help baby sleep by reading books or singing lullabies.
The researchers recommend that manufactures lower the maximum volume, include automatic timers to shut off the devices and insert printed warnings about noise-induced hearing loss.
The researchers did not reveal the names of the tested machines, and several individual manufactures declined to comment. In a statement, the U.S.-based Juvenile Products Manufacturers Association said its members "welcome any and all information that will advance the safety and well being of children" and use that information, when applicable, "in the safety and design of products."