Have you ever noticed that babies can fall asleep in some of the noisiest places? At home, you can keep everything calm and quiet, while the baby screams her head off, but in a crowded restaurant, or even at a sporting event, baby is able to fall right to sleep, despite the noise.

Turns out there may be a very logical reason for that. While baby was in your womb, she was subject to constant stimulation. Every time you moved, even a little, she was jostled about and rocked back and forth. And as it turns out, it’s actually fairly loud inside Mamma’s tummy.

As early as the 9th week of pregnancy, your baby was able to not only hear, but react to sound. By the end of week 26 (the end of the second trimester), your baby’s hearing is almost fully developed.

During your baby’s entire stay inside of you, she is surrounded by constant noise. Your body’s inner workings make identifiable sounds all day, every day. Even while you sleep, baby is surrounded by the sounds of your breathing, digesting, and the constant, gentle thump, thump of your heartbeat. All of this lends a certain rhythm to your baby’s existence. Believe it or not, part of what is scary to your baby after she is born is the lack of noise in the outside world.

One of the best things you can do to soothe your baby and help her fall asleep is to provide some form of noise. The best sounds include a lot of “white noise,” as these sounds are most reminiscent of the way things sounded inside the womb, when everything was muffled by embryonic fluids.

You can buy commercial white noise machines, if you like. Some of them are even designed specifically to replicate the sounds from inside the womb, which baby is sure to find comforting. Other things you can do to create white noise and soothe your baby include running household machinery or appliances near her, such as the laundry machine, vacuum cleaner, or fans. Make sure that you don’t leave baby unattended, of course, especially after she has become mobile.

Fans are perhaps the best option, as running a fan in the room also helps with air circulation which is believed to lower the risk of SIDS. Place the fan so that it is parallel with your baby (not blowing directly at or away from her) and make sure that it is far enough away that she can’t get her hands or feet near it.

Of course, loud, sudden noises will startle baby, so it’s best to avoid those. But constant white noise is one of the best sleep aids you will ever find for your baby, especially if she is fussy or has colic.