The sound of silence is rare in a household with a baby. In an attempt to soothe their infant to sleep, many parents turn to sound machines to produce nature sounds or white noise … but how much noise is too much?

A new study reported in the journal Pediatrics shows that some sound machines can produce noises so loud that they exceed safe levels for adults, let alone infants. In fact, some sounds could damage infants’ hearing and hinder auditory development.

Researchers tested 14 infant sleep machines at maximum volume from different distances. Three of the machines produced sound greater than the recommended decibel level. If the device were played continuously for eight hours, infants would be exposed to sound levels higher than those recommended for adults.

The study recommends parents place the sound machines as far away from their infant as possible, and play the noises at a low volume for a short time. One pediatrician says parents should make the noises as quiet as a soft shower and keep the machine at least a foot away from the child’s head.

The main issue is how loud the machines can be, not how long a baby is exposed to the noise. A baby’s ear is smaller than an adult’s, so higher-frequency sounds are often amplified. Studies on animals have suggested that age-related hearing loss may be a result of early exposure to noise.

Low-pitched, rumbly sounds are recommended for a baby’s sleep, as they are reminiscent of the baby’s time in the womb.

Experts disagree about the usefulness of these machines and what recommendations should be given for them. But although the long-term effects of masking environmental sounds in infants is unknown, one thing is clear — a good night’s sleep is crucial for both baby and parents.