White noise helps you fall asleep by masking background noise that would otherwise prevent you from sleeping. For this reason, a white noise machines have been found to help people sleep.
The science: A 2001 study found that white noise made it easier to fall asleep and stay asleep (Borkowski et al., 2001). Another study found that white noise made it easier to stay asleep in otherwise distracting environmental noise, such as with the noise of the intensive care unit (ICU) (Stanchina et al., 2005).