White noise machines are everywhere in nurseries, and so is a headline claiming they damage babies’ hearing. Both the enthusiasm and the alarm outrun the evidence. Here is what was actually measured.
The study
In 2014, researchers tested fourteen infant sound machines sold in North America, playing each at maximum volume and measuring the output at three distances: thirty centimetres (roughly on the crib rail), one metre (on a nearby table), and two metres (across the room).
All fourteen machines exceeded 50 decibels — the level recommended as a limit for hospital nursery noise — at both thirty centimetres and one metre. Thirteen of the fourteen still exceeded it at two metres. Three machines, at thirty centimetres, exceeded 85 decibels, which is the threshold used for adult workplace noise-exposure rules. The averages were about 79 decibels at thirty centimetres, 70 at one metre and 63 at two metres.
What it did not measure
The study measured the maximum output of the devices. It did not measure how loud parents actually run them, how long babies are exposed, or any hearing outcome in any child. The 85-decibel comparison is to an adult occupational standard, not to an infant safety threshold. So the honest reading is not “sound machines cause hearing loss” — that study does not show it — but “these machines can produce more than people assume, so treat them with a little respect”.
The authors’ own recommendations were modest and practical, and they are the ones worth following.
The four rules
- Not in the crib, and not on the crib rail. Put it as far from the baby as is practical — across the room is fine. Distance is the cheapest volume control there is.
- Low volume. You should be able to hold a normal conversation over it, and you should be able to hear your baby over it. The “as loud as a vacuum cleaner” advice comes from measurements of sound inside the womb and is not a safety standard for a postnatal ear.
- Time-limited. Use it to help with settling and for the first stretch, rather than at full volume for twelve hours. Many machines have a timer.
- It is a tool, not a fix. There is some evidence that steady sound helps some babies settle, and it is useful for masking a noisy household or an older sibling. It is not on the short list of things with strong evidence, and it is not required.
A note on what does have strong evidence
If you are choosing where to put your energy, the sound machine is a small lever. The large ones at any age are a short, consistent bedtime routine — the best-supported intervention in the field — bright days and a properly dark room at night, and safe sleep for every sleep. Get those right, and the sound machine is a matter of taste.
This is parenting information, not medical advice. If you have any concern about your baby’s hearing, ask your pediatrician.