They might be helping put the little ones to sleep, but exposing them too early and too long to those infant sleep machines (ISMs) may prove to be counter-beneficial in the long term for babies' sensitive hearing.
Researchers at Canada's University of Toronto said these ISMs supposedly drown out other forms of noise so babies can get a good night's sleep. They pipe in sounds such as rain, birds chirping or a heartbeat, as well as provide background noise to drown out other loud or annoying sounds.
But without knowing, parents with the aid of those ISMs are actually putting more into an already noisy environment "without even thinking about the amount," Dr Blake Papsin, a study author and otolaryngologist-in-chief at The Hospital for Sick Children in Toronto, told LiveScience.
Moreover, using the machines on a regular basis may produce sound levels that can lead to hearing, speech or learning problems.
For their study, the Canadian researchers gathered 14 different types of ISMs that produced a range of different sounds from a heartbeat to traffic, white noise, fire, rain, and oceans. They were placed at different distances near and away from the crib.
According to researchers, the safe noise recommendations implemented by hospital nurseries was a limit of 50 A-weighted dB (dBA) averaged over an hour.
Played at maximum volume to eradicate the other present noise that could disturb baby's sleep, it was found that 3 of the 14 machines produced noise louder than 85 dBA at a distance of only 30 cm, the maximum safe level set by Canadian and US agencies overseeing occupational safety and health for adults working an 8-hour shift.
"These machines are capable of delivering noise that we think is unsafe for full-grown adults in mines," Mr Papsin said.
At distances of 30 and 100 cm, all 14 ISMs exceeded 50 dBA, while at a distance of 200 cm, 13 of 14 ISMs could produce noise above 50 dBA.
ISMs are marketed as able to produce soothing ambient noise that will mask other disruptive environmental sounds while babies sleep. Makers have advised parents that for best sleeping results, they should operate the machines for the full duration while the baby sleeps, setting volume levels as high to mask an infant's cry.
However, this could create problems for the baby's hearing, speech or learning problems.
"Most parents assume the sleep machines are safe," Mr Papsin said. "The sounds that resonate best with a baby are the sweet sounds of Mom and Dad."