Parents-to-be may want to think twice before putting an infant sleep machine on their baby registry. The sound-generating devices might help lull a little one to sleep, but a new study suggests the noise may be harmful to a baby's hearing.

Canadian researchers have found that when noise machines are used on a regular basis, they can produce sound levels that can be dangerous for infants' ears, which may lead to hearing, speech or learning problems.

"I'm not saying that these devices will cause hearing loss — I'm just saying that they could," said Dr. Blake Papsin, a study author and otolaryngologist-in-chief at The Hospital for Sick Children in Toronto.

Infant sleep machines pipe in sounds such as rain, birds chirping or a heartbeat, to soothe a baby to sleep. They also provide background noise to drown out other loud or annoying sounds that might keep an infant up at night. (Apps that play baby-friendly sleep sounds are also available for computers or mobile phones, but were not included in this research.)

However, by using infant sound machines, "people are taking a noisy environment and adding more noise to it, without even thinking about the amount," Papsin told LiveScience.

Sound exposure

In the study, the researchers tested 14 different infant sound machines, measuring the sound levels produced when each model was set at maximum volume and placed at three distances from where an infant would sleep, simulating its location in a baby's room.

Sound levels were checked at about 1 foot from the machine (similar to mounting the machine on a crib rail), more than 3 feet (placing it near a crib, for example on a nightstand), or more than 6.5 feet away (putting the device across the room).

The results revealed that all 14 machines produced sound levels that exceeded acceptable noise limits for infants in hospital nurseries. Three machines generated potentially harmful levels of sound, that surpassed allowable limits for adult workplace noise, when placed on a crib rail.

All but one model topped the decibel limits recommended for hospital nurseries even at an across-the-room distance, according to the study published online today (Mar. 3), which will appear in the April issue of the journal Pediatrics.

Regular exposure to these sound volumes may put babies at risk of developing noise-induced hearing loss, according to the researchers.

Besides being smaller and still developing, the ear canal of an infant is a little wider and a little straighter than that of an adult, he said. This amplifies higher-pitched sounds.

"The sounds that resonate best with a baby are the sweet sounds of Mom and Dad," Papsin said.

He said he wants parents and caregivers to be aware that while it's safe for infants to be around sound and noise, there is a "dose" of sound that could harm babies hearing.

He hopes these findings generate a conversation about what "dose" of sound parents want their baby exposed to. He also suggests parents imagine the ideal sleep environment for their son or daughter, then work hard to recreate those quiet surroundings.

Safe sound

"Most parents assume the sleep machines are safe," Papsin said. And it's common for parents to underestimate how much volume a baby's ears are truly getting, he added.

Papsin said the best sounds for infants' ears are soft, highly informational sounds, such as a Mom's soothing voice or snuggling a baby close to Dad's chest to hear his heartbeat.

The researchers would like to see manufacturers of infant sleep machines print a warning about noise-induced hearing loss on the box, and set a limit on the device's maximum volume, according to the study. They also want sleep machines to have mandatory timers and automatic shut-off features.

Because today's machines might offer parents few guidelines on safe usage, Papsin suggests the following tips:

Place the machine as far away from the baby as possible.

Never put it in the crib or on a crib rail.

Play it on the lowest volume and for the shortest duration possible.

Once a baby has fallen asleep, turn the device off.

This article originally published at LiveScience here