Infant sound machines have become a staple in baby registries with soothing sounds, including lullabies, nature sounds, and white noise aimed to put a baby soundly to sleep. The sound-generating devices may help babies fall asleep and give parents a good night’s rest, but they may do more harm than good in the long run. According to a study in journal Pediatrics, sound machines at maximum volume that exceed safe levels of 50 decibels (dBA) can potentially damage babies’ hearing and harm their auditory development.

On average, babies between the ages of 1 month to 12 months, should get 14 to 16 hours of sleep each night. At first, a baby has short stretches of three to four hours of sleep while they adapt to the different life rhythms outside the womb. To adjust a baby’s body clock toward sleeping at night, KidsHealth says, parents should avoid stimulation such as bright lights, playing, or talking with their baby during nighttime feeds as a way to reinforce the idea that nighttime is for sleeping. Babies may act fussy and not comprehend a bedtime routine right away, so a sleeping aid, such as a white noise machine, is usually used to lull them to sleep.

Although counter intuitive, white noise is meant to blend outside sounds into the overall background noise so the brain is less alert, and therefore, can help a baby sleep. Babies and adults mask the exterior sounds when they add white noise to their sleeping environment. The white noise signal works by drowning out the exterior sounds, also known as sound masking. Since babies have an immature nervous system and sensitive hearing, they are easily startled by loud noise. However, a noise machine can mask these sounds when at an acceptable volume.

Dr. Blake Papsin, Canadian lead author from the Hospital for Sick Children in Toronto, and his colleagues believe although sleep machines can increase uninterrupted sleep for babies, frequent use can lead to noise-induced hearing loss. Fourteen different types of white noise machines — widely available in the U.S. and Canada — were bought from off the Internet and in stores to measure maximum sound outputs. The machines play a total of 65 different sounds, including white noise, nature, mechanical, and heartbeat sounds.

The researchers utilized a sound booth to test each device when turned to its maximum volume and placed the sound meters at various distances: 30 centimeters away on a crib rail, 100 centimeters near a crib, and 200 centimeters across a baby’s room. The sound measurements were adjusted to see the effect they would have on a 6-month-old’s ear canal, wrote the researchers in their report. The ear canal volume is significantly smaller in infants and young children. According to the Boys Town National Research Hospital, a baby’s ear canal grows rapidly in the first few years of life but does not reach adult-like values until about 7 years of age.

The findings revealed each of the 14 machines in the study exceeded 50 dBA — the recommended noise limit for children in hospitals — but one of the machines exceeded safety levels when measured across the room at 200 centimeters. In addition, three of the sound machines had an output greater than 85 dBA, CNN reported. If these particular sound devices were on for eight hours, infants would be exposed to sound pressure levels that surpass occupational noise limits for adults.

"Most parents assume the sleep machines are safe," Papsin told LiveScience. “And it's common for parents to underestimate how much volume a baby's ears are truly getting.” The lead author believes the best sounds for an infant's ears are the soft and highly informative sounds of parents' voices, or even hearing a heartbeat.

The study highlights the potential danger the consistent use of sound machines have on a baby’s hearing. Papsin and his colleagues believe manufacturers should limit the maximum output level of their machines and print warnings on packaging about noise-induced hearing loss. They also suggest sleep machines come with mandatory timers and automatic shut-off features.

While it may take a considerable amount of time for manufacturers to make these changes, parents can actively limit their child’s exposure to the deafening machines. Simple tips parents can follow are placing the sound machines far away from their babies’ cribs, play them at low volumes for the shortest duration, and turn the device off as soon as the baby falls asleep. Papsin’s takeaway message is parents should consider these sleep machines in terms of dose.

Source: Cushing SL, Gordon KA, Hugh SC, et al. Infant Sleep Machines and Hazardous Sound Pressure Levels. Pediatrics. 2014.