Have you ever noticed that you sleep better with a fan on? Or, perhaps you rest well when the heater or air conditioner is running. It’s even possible that you often fall asleep when traveling on an airplane or a train, and it turns out there’s a scientific reason behind it — white noise.

White noise is defined as a noise containing many frequencies, all with equal intensities, according to Bill Fish, the Managing Editor of SleepFoundation.org. Fish is also a Certified Sleep Science Coach, and he says that, in general, white noise is background noise that tends to soothe us in some way.

Most of us don’t sleep in perfect silence. We live in cities with loud neighbors, barking dogs, and noisy traffic, and those disturbances often cause sleep problems for a lot of people. Even if you live off the grid you might be disturbed by the nocturnal sounds of nature, like critters running back and forth on the roof in the early hours of the morning, and loud choruses of chirping birds at sunrise.

A 2014 study published in Sleep Science, a scientific journal, noted that city noise, particularly that caused by transportation (trains, elevated subways or rail, cars, garbage trucks, etc.) can cause significant sleep disturbances, resulting in “cardiometabolic, psychiatric and social negative outcomes both in adults and children. Nocturnal environmental noise also provokes measurable biological changes in the form of a stress response, and clearly affects sleep architecture, as well as subjective sleep quality. These sleep perturbations are similar in their nature to those observed in endogenous sleep disorders,” according to the study. Here’s everything you need to know about white noise and sleep.

Read my story and see the complete Sleep Series over at Shondaland.