I returned yesterday from a long transpacific journey to find many messages from clients concerned for their children’s safety. The cause of their concern was major media coverage of a research article just published in Pediatrics. The article seemed to indicate that sleep sound machines pose a risk to babies’ hearing. You can read the original article here.
I, too, was initially alarmed to learn about the potential danger to children’s hearing. I use them in my own home as well as recommend them to my clients.
After carefully reviewing the original article and doing some additional research of my own, here’s my interpretation of the research presented.
The study measured noise levels from 14 white noise machines (which the researchers termed Infant Sound Machines). The authors did not name any specific brands and models. The machines ran at their highest volume and noise levels were measured at 30, 100, and 200 cm from each machine. These distances are, roughly, that between baby and machine when placed on a crib rail, beside the crib on a bedside table, and across an average-sized nursery.
The researchers used a sustained noise level limit of 50 A-weighted decibels (50 dBA) as a measurement standard. This is the recommended level for hospital nurseries and neonatal intensive care units (NICU’s). The study also referred to a recommendation by the Canadian Centre for Occupational Health and Safety. The recommendation states that workers should avoid exposure to sustained noise levels greater than 85 dBA for more than 8 hours.
The study found that 13 out of 14 of the machines, when turned to maximum volume, produced noise levels greater than 50 dBA at a distance of 200 cm (i.e. across the room). Three of the machines produced levels greater than 85 dbA at a distance of 30 cm (i.e.right at the crib rail).
At first glance, these results seem alarming indeed. But it’s important to look beyond first glance.
The recommended limit of 50 A-dB for hospital nurseries and NICU’s was put in place to protect newborn and/or health-compromised babies. It is also a place where there is a good deal of machinery around to create a lot of noise.
An environment with 50 A-dB ambient noise is pretty darn quiet. A room with no perceptible noise except the hum of a lightbulb and 2 people breathing measure at about 45 dBA. The room where I’m currently sitting, with a small fire gently crackling in the fireplace and my tiny computer fan whirring 30 cm from the sound measuring device, registers at 49 dBA. Sitting on a porch on a quiet street, with chirping birds and traffic in the distance, will expose you to about 55 dBA. A muted conversation in the background registers at about 60 dBA. Riding inside a car (without the stereo on and with the windows closed) averages around 70 dBA.
Therefore, the results of the research study under discussion tell me that:
* Playing any of the sleep sound machines used in the study at maximum volume 200 cm (across a small room) produces a moderate noise level. This level is equivalent to somewhere in the range between sitting on a front porch on a quiet street with little traffic and riding in a car with the stereo off (depending on which model you’re using).
* These noise levels are greater than a very conservative limit recommended for hospital nurseries.
* In the case 3 of the 14 machines, placing that machine right at a baby’s crib rail at maximum volume is likely to expose them to noise levels higher than that recommended for adult workers. This is potentially concerning.
We should not leave sleep sound machines directly next to babies at maximum volume for extended periods of time. To some, this may seem like an issue of simple common sense. I was surprised to read a statement in the Pediatrics article that sleep sound machines are designed to be placed on a crib rail. Few sound machines are designed for this placement, aside from one or two which I don’t recommend. For one thing, it is not safe to attach or place any foreign objects on a crib rail or inside an infant’s crib.
Since sleep sound machines are marketed for use with babies, I wholeheartedly agree with study’s authors’ suggestion that we develop use guidelines and volume limits for these products. Clearly, it’s important to avoid placing sound machines too close to infants or operating them at a potentially harmful noise level.
Sound machine manufacturers don’t currently provide information about their sound output levels. However, you can measure them yourself by downloading a noise meter app onto your mobile device. You might find it interesting to measure other sound levels in your own environment to get an idea of the sound levels you and and your family experience regularly.
How do the machines I recommend measure up?
I used the Decibel Meter Pro app on an iPhone 4S to measure various sounds around my home. I also measured output from the two sound machines I currently recommend: The HoMedics SS-2000G/F-AMZ Sound Spa and the Marpac Dohm-DS Dual Speed Sound Conditioner.
At the maximum volume setting, with the iPhone microphone at 30 centimeters from each sound machine, the average dBA readings over a 30 second period were 66 and 64, respectively. At 200 centimeters the average readings were 53 and 50 dBA.
Clearly, the readings at 30 cm were higher than the 50dBA limit that has been recommended for hospital nurseries and NICU’s. Firstly, as mentioned above, no one should be placing a sound machine that close to their baby. Secondly, I’m not sure exactly how useful this is as a general guideline for noise exposure. I’m not sure how many actual nurseries and NICU’s in operation would actually be able meet this requirement. I was only able to register any readings below 50dBA in a few small areas of my rather quiet home.
In any case, at a distance of 200 cm, the Marpac did measure just at 50dBA at its very highest setting. The device is adjustable in a few different dimensions so I set it at the higher fan speed, then adjusted the other features until I found the very highest dBA reading. The HoMedic device did register slightly above the proposed NICU limit when turned up all the way on the “White Noise” setting. But dialing the volume down slightly from maximum, (approximately 10 degrees on the circular dial), brought it down to below 50 dBA.
So, are they safe?
It appears that either machine, when placed 200 cm (about 6.5 feet) from the baby and set at or close to the maximum volume, manages to meet what I see as a very conservative noise limit. I also think there is room for reasonable people to disagree over whether any sound levels higher than 50 dBA are harmful to hearing, even for sustained periods. Otherwise we may need to avoid any sustained moderate noise from things like distant traffic, air conditioners, background conversation, and car rides. But, in the absence of hard evidence, it makes sense to be conservative and cautious. So, again, using either the Marpac at its highest volume, or the HoMedics a bit below that on the White Noise setting, at least 6.5 feet away from where baby is sleeping should meet the safety standard proposed by the article’s authors.
Of course, this assumes that the readings I took were accurate. It would help to have testing done using more sophisticated equipment. So, for the sake of maximum caution, you could choose to either turn the volume down a bit more, or move the machine a little farther away. You can also do your own volume readings. Just make sure your readings are A-weighted, since, according the the Pediatrics study’s authors, measures the frequency range most likely to cause hearing issues.
Do baby sleep professionals really recommend high-volume white noise?
I would also like to comment on a point brought up in the introduction of the article. It stated that many “baby sleep experts” recommend exposing babies to white noise “at a volume equal to or louder than an infant’s cry“. The article cited a book by Dr. Harvey Karp as the source for this recommendation. It seemed to imply that Dr. Karp and others recommend exposing babies to loud noise for sustained periods of time, which is incorrect.
Dr. Karp and others have suggested using white noise which matches the intensity of a baby’s crying or fussing for very short periods of time to help calm the baby. The rationale for brief exposure to high-volume white noise is that a crying baby can’t be soothed by a sound it can’t hear over its own crying. As soon as the baby starts to calm, any “shhhing” or other soothing noise should decrease in intensity, either to a lower volume or completely. But, since the authors of the Pediatrics article misconstrued Dr. Karp’s recommendations, perhaps he should spell out more clearly exactly what levels of white noise are ok, and for how long.
What I recommend:
To review, at this time I can recommend the following two white noise machines: The HoMedics SS-2000G/F-AMZ Sound Spa (on the white noise setting); and the Marpac Dohm-DS Dual Speed Sound Conditioner. When placed 6.5 feet or more from the crib, the Marpac complies with the noise limit proposed by the study’s authors at any setting. The HoMedics can be used at slightly below the maximum volume setting or slightly further away. I believe these limits are conservative and am comfortable continuing to use sleep sound machines as a small piece of the comprehensive sleep support I provide.
Note: I limit my recommendations to these two machines because I have measured their noise levels. I imagine that there are many others that are also safe to use.
I appreciate this study for bringing to light the potential harm that overexposure to noise may pose to babies’ hearing. I look forward to seeing more research and discussion on this topic.
Where do we go from here?
It’s important that manufacturers, health professionals and parents be informed about how to use these products correctly and safely. More clear guidelines and standards for their use would be a step in the right direction.
Establishing and maintaining healthy sleep is a complex process and many different factors contribute to its success. There is no single product or magic solution that will help any baby or family sleep well.
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