The white noise machines that lull babies to sleep could be hurting their ears.  

A study published in the journal "Pediatrics" reports infant sleep machines, if used for too long or at maximum volume, could damage a baby's hearing.  

Researchers recommend only playing the machines quietly for a short period of time, and as far from the baby as possible.  

At distances of one foot and three feet, the maximum volume of each white noise device was higher than the recommended noise limit for hospital nurseries.