My conclusion is that always use things with moderation. I feel that having a sound machine is useful during initial sleep training, however, once sleep training is complete, I recommend eliminating the sound machine so that the infant can get accustomed to sleeping without an additional crutch. Then, you can use the sound machine on certain occasions to drown out outside noises, for instance during a thunderstorm, a noisy get together that may affect your child’s sleep or house guests.
Recent study published in Pediatrics journal:
Infant Sleep Machines and Hazardous Sound Pressure Levels
BACKGROUND AND OBJECTIVE: Infant “sleep machines” (ISMs) produce ambient noise or noise to mask other sounds in an infant’s room with the goal of increasing uninterrupted sleep. We suggest that the consistent use of these devices raises concerns for increasing an infant’s risk of noise-induced hearing loss. We therefore sought to determine the maximum output levels of these sleep machines.
METHODS: Sound levels of 14 ISMs played at maximum volume were measured at 30, 100, and 200 cm from the machine using correction factors to account for a 6-month-old’s ear canal.
RESULTS: Maximum sound levels at 30 cm were >50 A-weighted dB for all devices, which is the current recommended noise limit for infants in hospital nurseries. Three machines produced output levels >85 A-weighted dB, which, if played at these levels for >8 hours, exceeds current occupational limits for accumulated noise exposure in adults and risks noise-induced hearing loss.
CONCLUSIONS: ISMs are capable of producing output sound pressure levels that may be damaging to infant hearing and auditory development. We outline recommendations for safer operation of these machines.