Why does my baby sleep better with the bathroom fan on?

Your baby sleeps better with the bathroom fan on primarily because of womb mimicry and sound masking.

1. Womb Mimicry

Inside the womb, babies are constantly exposed to loud, low-frequency rushing sounds from your blood flow and heartbeat—often measuring around 70 to 80 decibels (about as loud as a vacuum cleaner). The continuous, deep hum of a bathroom fan mimics this comforting, familiar environment, which naturally triggers a baby's calming reflex.

2. Sound Masking

Babies have brief sleep cycles (about 40–50 minutes) and spend a large portion of their sleep in active REM sleep, where they are easily startled. The continuous "white noise" of the fan masks sudden household noises—such as footsteps, clanging dishes, or a barking dog—preventing these sudden spikes in volume from waking them up.

3. Clear Sleep Association

Consistency is key for infant sleep. Over time, the sound of the fan becomes a powerful psychological cue (sleep association) that tells your baby’s brain it is time to wind down and sleep.