"Infant sleep machines" could damage babies' hearing

Sleep machines are devices designed placed next to the baby's crib and designed to help babies sleep more soundly. They work by generating ambient or "white" noise, masking other noises from around the house or outside that could disturb the baby. Websites promoting these machines often suggest that parents and childminders should have the device on continually while a child is sleeping: a common recommendation is that the volume of the sounds played by the machine should be equal to or louder than the cry of an infant. Many parents say their babies become so used to the sounds of rainfall or birds that they will not nap without them.

But researchers at the University of Toronto evaluated 14 popular sleep machines at maximum volume and found they produced between 68.8 to 92.9 decibels at 30 centimeters, about the distance one might be placed from an infant’s head. Three exceeded 85 decibels, the workplace safety limit for adults on an eight-hour shift for accumulated exposure as determined by National Institute for Occupational Safety and Health. One machine was so loud that two hours of use would exceed workplace noise limits.

At 100 centimeters, all the machines tested were louder than the 50-decibel limit averaged over an hour set for hospital nurseries in 1999 by an expert panel concerned with improving newborn sleep and their speech intelligibility. 

As infants are still developing and have much smaller ear canals than adults, it is possible that babies are more susceptible to the adverse effects of noise levels than adults.

The researchers think that safe use of these devices could be possible, but only with policy recommendations that set appropriate limits on the manufacture and use of the devices.

They recommend that families using infant sleep machines should place the device as far away as possible from the baby, and never in the crib or on the rail of the crib, only play the sleep machine at a low volume and only play the sleep machine for a short duration of time.
The study authors also recommended that manufacturers limit the maximum noise level of infant sleep machines. 

Another concern briefly raised in the Pediatrics study is whether listening to white noise can be detrimental to auditory development. A 2003 study published in the journal Science found continuous white noise delayed development of the brain’s hearing center in newborn rats.

In humans, the brain of a newborn is learning to differentiate sounds at different pitches even during sleep, said Lisa L. Hunter, scientific director of research in the division of audiology at Cincinnati Children’s Hospital.

“If you’ve conditioned them to white noise, there’s every indication that they might not be as responsive as they otherwise should be to soft speech,” she said.

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References:
Infant Sleep Machines and Hazardous Sound Pressure Levels: PEDIATRICS ( journal of the American Academy of Pediatrics); March 3, 2014