courtesy Carmen Wilson Photography
(CNN) -- Parents: You want your baby to sleep soundly so that you can sleep too, right?
So maybe you bought a
machine that will play soothing sounds in the nursery. And maybe you
crank up the volume so that your kid doesn't hear sirens outside or
But how loud should these
machines be? How long should you keep them running? Should you put them
close to your baby's ears, or on the other side of the room?
A new study in the
journal Pediatrics suggests that some noise machines have the ability to
produce sounds so loud that they exceed safe levels for adults, let
alone infants, and therefore could potentially damage infants' hearing
and hinder auditory development.
However, it's important
to note that the goal of the study was to measure the maximum effective
output levels -- not to observe direct effects on children. Experts
disagree on what recommendations should be given on using these
"These machines are
capable of delivering enough of a dose over a period of time to
theoretically cause hearing loss, but that's not been tested," said the
study's senior author Dr. Blake Papsin, who is affiliated with the
University of Toronto and the Hospital for Sick Children in Toronto.
Researchers tested 14
infant sleep machines at maximum volume, analyzing the noise level
production from distances of 30, 100 and 200 centimeters. The
30-centimeter measurement resembles a typical distance from a baby's
head to the crib rail; 100 centimeters would be near a crib and 200
centimeters would be across the room from a crib.
The particular machines
are not named in the study, but researchers said they are "widely
available in the United States and Canada." Papsin declined to reveal
which products were used.
These machines play a
total of 65 different sounds, including white noise, "nature" sounds,
mechanical sounds and heartbeat sounds.
Hands-off approaches OK for sleepless infants, study says
Hospital nurseries and
neonatal intensive care units have set a noise equivalent of 50 decibels
on average over the course of an hour, according to the study. Canadian
and U.S. occupational health and safety authorities have recommended a
workplace limit of 85 decibels over eight hours for adults.
Three of the infant
sleep machines in this study had outputs greater than 85 decibels, which
exceeds that recommendation. Additionally, if these sound devices were
played continuously for an eight-hour period, the researchers wrote,
"infants would be exposed to sound pressure levels that exceed
occupational noise limits" for that time period for adults.
The study authors
recommend manufacturers be required to limit maximum sound output levels
of such machines, print warnings about noise-induced hearing loss on
the packaging and include a timer that would shut the device off after a
They also recommend
families place these infant sound machines as far away as possible from
the infant -- never on the crib rail or in the crib, the study said. The
machines should be played at a low volume and for a short time, study
But wait a minute! Don't we want unwanted noises blocked from infants' ears all night long?
Dr. Harvey Karp,
pediatrician and author of books including "The Happiest Baby on the
Block" and "The Happiest Baby Guide to Great Sleep," says he has
concerns about some of the study's conclusions.
It's true that intensity
of sound is important to consider, he said. Concretely, parents should
look to make these machines as loud as "a soft shower," he said, and
keep them at least a foot (30 centimeters) away from the child's head.
But as far as only using
an infant sleep machine for a short time, that recommendation is
misinformed and is" not supported by the data in the study," he said.
Karp instead recommends
keeping the noise going for the entire duration of sleep, because
otherwise the baby will have more disturbances in the middle of the
"The white noise is there as a continual presence, just like a teddy bear," Karp said. "It's like a teddy bear of sounds."
Papsin stands by the
opposite recommendation in the study, saying that using infant sleep
machines over eight-hour stretches is not supported by scientific
Dr. Harvey Karp: Sleeping babies and kids make happy parents
Karp points out the
Pediatrics study did not directly address this question with data, nor
does it give an overall assessment of risk. Papsin and colleagues were
not able to give an estimate of how those risks would weigh against the
benefits of the noise devices, either.
The Juvenile Products Manufacturers Association,
a trade organization representing manufacturers of 95% of prenatal to
preschool products, responded to the study in a statement: "JPMA
encourages parents to follow manufacturer guidance and instructions, and
to use products as designed and intended. The safety and care of
children is JPMA's highest priority."
So what's a parent supposed to do?
There just hasn't been a
lot of research into this question of what effect these infant noise
machines have, says Patti Martin, director of audiology and speech
pathology at Arkansas Children's Hospital.
Her bottom line: The
issue with the machines is how loud they are, not the amount of time
they are used. She also likes the idea of keeping the machines out of
the crib because closer noises sound louder to the developing auditory
An infant's ear canal is
smaller than an adult's, so in babies higher-frequency sounds are
amplified, the study said. Evidence from animal studies suggests that
risk for age-relating hearing loss may result from early exposure to
sounds are better for a baby's sleep, Karp says, as they are
"reminiscent of the experience in the womb." Exposing the infant to very
loud sounds in short spurts is fine -- a baby's own cry is 10 times
louder than a hair dryer! -- but for promoting sleep, he says, aim for
softer and lower-pitched.
Of course, there are other ways to soothe your child to sleep, such as swaddling or holding a baby close, Martin says.
Depression and baby sleep: Vicious cycle?
No one knows the
long-term implications of masking environmental sounds in infants, in
terms of how they will learn later in a noisy environment, Martin says.
On the other hand, a good night's sleep for baby is critical for the health of both parent and child.
"From a safety issue,
from a nutrition issue, from a growth issue, all of those sorts of
things -- sleep is critical for them," she says. "There will always be a
group of babies that require a little extra something."
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