If you, like me, have used a white-noise machine to help your wee one sleep, you probably had a panic attack when you saw the headlines Monday morning. “Warning: Infant sound machines may lead to hearing loss,” screamed CBSNews.com. “Popular Infant Sound Machines May Be Hazardous to Babies' Hearing,” warned the Huffington Post. Similar scare stories appeared on the websites of Fox News and USA Today. My favorite was Health Newsline's headline, which claimed that sleep machines can cause deafness.
These stories were all based on the results of a single study published in Pediatrics. And although the study raised questions about how white-noise machines should be used, it didn't show that the machines caused hearing loss or deafness. In fact, “not a single infant was harmed in the study,” explains lead author Blake Papsin, a pediatric otolaryngologist at Toronto's Hospital for Sick Children — because no babies were involved in the study. Moreover, many of the articles covering the study emphasized that every single one of the sound machines exceeded a “recommended noise limit,” yet this limit has nothing to do with infant safety or hearing loss at all.
First, let me briefly describe the study. Papsin and his colleagues at the University of Toronto and the Hospital for Sick Children tested the loudness of 65 white-noise sounds emitted by 14 infant sleep machines when these machines were set to maximum volume. They recorded how loud the machines would be when placed a little under a foot from an infant's ears — if, say, you put a sleep machine inside your child's crib or mounted it on the crib rail — as well as how loud the machines would be when they were placed 3 1/4 feet or 6 1/2 feet from infants' ears — so, on the nightstand. They made mathematical corrections to account for the fact that an infant's ear canal responds to sounds differently than an adult's does. Overall, they found that, at maximum volume, every one of the noise machines placed within 3 1/4 feet of infants' ears were capable of producing sounds that exposed the babies to more than 50 A-weighted decibels, what the study describes as “the current recommended noise limit for infants in hospital nurseries.”
That sounds bad, right? Well, I was curious about this “recommended noise limit,” so I did some digging — and it turns out that the limit, recommended in 1999 by the National Resource Center, has nothing to do with protecting infants' hearing. It was set for neonatal intensive care units, or NICUs, with the primary objective being “to preserve a large portion of each hour for infant sleep.” Sleep is crucial for premature infants, and loud noises startle and bother NICU babies more than they disturb full-term healthy babies, so the limit primarily exists to help premature babies snooze better. That's funny, because helping babies sleep better is, of course, exactly why parents use white noise machines. The 1999 report even addressed whether loud NICUs might hurt premature infants' ears and concluded that, “not surprisingly,” harmful effects from loud NICU noise “have not been demonstrated consistently.”
And white-noise machines do seem to help babies sleep better. The idea behind white noise is that it masks sudden sounds (doorbell, dog barking, older brother screaming), making it easier for babies — and, well, everyone — to fall and stay asleep. One small trial found, for instance, that more than three-quarters of newborns fell asleep within five minutes when they were exposed to white noise, compared with only a quarter of newborns who tried to fall asleep without it.
So did the study raise any cause for concern? Yes. The researchers found that three of the 65 sounds emitted by these 14 sound machines, when turned all the way up and placed within a foot of infants' ears, would bombard infants with a noise level exceeding 85 A-weighted decibels, a safety limit set by the U.S. National Institute for Occupational Safety and Health for workers exposed for eight-hour stretches. (For comparison, 50 decibels is the sound level associated with moderate rainfall; 60 decibels corresponds to the noise of typical conversation; 70 decibels is comparable to the sound of a vacuum cleaner; and blenders and blow-dryers emit 80 to 90 decibels. Don't beat yourself up, parents who have used the vacuum cleaner as a noise machine while waiting for the real deal to arrive from Amazon.) The authors point out that the 85-decibel limit is, of course, set for adults, and so it may not be conservative enough for infants, whose developing ears might be more sensitive and prone to harm. In other words, 85-decibel white noise could very well be dangerous; unfortunately, the study did not name these obnoxiously loud brands, so there's no way to know which machines to avoid. There is, however, some controversy here, because when researchers stuck microphones in pregnant women's uteruses for a 1990 study I'm glad I wasn't a part of, they found that fetuses are exposed to between 72 and 88 decibels of baseline noise in the womb — the latter being about as loud as the maximum output of the white-noise machines tested in the study. Yet as far as I know, no one thinks of the womb as a dangerous environment. (Papsin, however, isn't convinced by the uterus-microphone study and says that no one really knows what goes on inside the womb and that the nature of the noise in there may be very different.)
So what do we know about the effects of white-noise machines on hearing? Not much. As the study itself points out, “hearing evaluations have not yet been systematically performed in a large group of children previously exposed to infant sleep machine noise.” Animal studies tell us very little too. One 2009 study found that when rats were exposed to 80 decibels of white noise, eight hours a day, for two weeks during the critical period in their hearing development, their neurons shifted in how they responded to stimuli, but the researchers did not test inner-ear function or other aspects of behavior or cognition, so it's unclear what that means. Another study found that rats' hearing became impaired when they were exposed to 100 or 110 decibels of broadband noise, eight hours a day, for five days, but that their hearing wasn't affected when they were exposed to 90 decibels.
Ultimately, Papsin says, his study is about dose: “The recommendations for parents is to use machines for as short a duration as possible, as reduced a volume as possible, and at the farthest distance from the baby as possible to get the desired effect,” he says. Those are his recommendations, based on his study's results, but they are not Gospel. And it's worth noting that, findings aside, Papsin is not a fan of white-noise machines — he sees them as a symptom of modern parenting gone bad. “Have we really come, as a society, to a point where we can't put our babies to bed without an app?” he asks. “Slow down, parents.” Maybe instead of using white-noise machines, he says, we should double-pane our windows, put down thick rugs, “or maybe move.”
So where does this leave us? Clearly we need more research on white noise. Until we get it, I'll turn my sound machine down a few notches and avoid letting my kid snuggle ear-to-speaker with those white-noise-making stuffed animals. But am I going to worry, based on this study, that I've caused my son irreparable hearing loss or swear off using a sound machine when baby No. 2 arrives? No. First, I don't know about you, but I've never put my sound machine on its most abrasive setting, turned it all the way up, and placed it within a foot of my son's ears for eight hours at a time. Second, while it's true that parents may not have needed white-noise machines 20 years ago or 2,000 years ago, the world is different now. And while it's important to consider risks when we make choices in how we raise our kids today, we shouldn't forget that these same choices can provide important benefits, and that the two need to be weighed together. I am certain that white noise has helped my son get a lot more shut-eye these last few years, and that this extra sleep has been undeniably good for his health and development — not to mention my sanity.