It’s science: This is why your baby always falls asleep in the car

Baby…go. to. sleep.

When your overtired, fussy baby’s crying is bringing tears to your own eyes, and no amount of soothing or Dr. Harvey Karp tips seem to be helping, it’s time to go for a drive. Safely secured into their car seat, your baby begins to settle. One more lap around the block ought to do it, you think, as you see your baby finally begin to drift off to sleep.

What is it about a car ride that seems to cast a spell on a wide-awake baby? Turns out, the inside of a moving car is a lot like the safe, warm and quiet environment inside your womb. The sound and vibration of a moving car’s engine creates the similar sound and motion that helps your baby relax.

Cars offer the same type of low-level rocking movement that your baby felt in your womb when you walked around.

Your baby’s response to rocking is a natural reaction of their sensorimotor systems. Researchers have found that gentle and constant rocking regulates your baby’s central, motor and cardiac systems in a coordinated way that calms them down.

Your baby’s cerebellum is the part of their brain that is most primitive—always on guard and keeping track of everything going on in their environment. It’s directly linked in a feedback loop with the vagus nerve, a part of the parasympathetic nervous system that connects the brainstem to the body and allows it to monitor and receive information. The parasympathetic nervous system oversees a vast array of crucial bodily functions, including the fight-or-flight response and heart rate. Rocking puts your baby’s cerebellum at ease and creates a parasympathetic response of relaxation, lower heart rate and increased sense of well-being.

The steady humming of your car’s engine is a type of white noise that is soothing to your baby.

White noise is sound that contains all frequencies at equal intensity and distribution. Your car’s engine is a kind of white noise that can mimic the familiar sounds your baby heard in your womb and can mask loud sounds that may stimulate your baby’s brain. White noise influences sleep by encouraging your baby’s brain to adopt and maintain the slower, rhythmic brain waves associated with sleep. In a small, randomized study published in the Archives of Disease in Childhood, full term newborns listened to recordings of intrauterine sounds. It was shown that listening to this type of white noise increased the likelihood of the babies falling asleep within five minutes from 25% to 80%!

The inside of your car is not very stimulating.

The inside of a car can be insulated, warm and dark, just like your womb. And the interior doesn’t change, so there is nothing new to see, hear, feel or do. Plus, your baby knows you are nearby and feels safe. This combination allows your baby to tune out the external world, relax completely and fall asleep.

The snugness of your baby’s car seat creates a feeling of security.

Not only does the car seat harness hold your baby’s body in the proper position in case of an accident, the feeling of security it provides and the cozy warmth of your car’s interior can utterly transport your baby back to the womb.

Coaxing your baby to sleep by taking a car ride can be an effective solution to sleeplessness, but is it safe?

A study published in the Journal of Pediatrics shows that when car seats are used as directed by the manufacturer’s guidelines, babies have a very low risk of suffocation or strangulation from the harness straps. Dr. Ben Hoffman, chairman of the American Academy of Pediatrics Council on Injury, Violence, and Poison Prevention Executive Committee, agrees, stating, “All the data that we have on car seats indicate that there aren’t risks associated with babies sleeping in the car for short periods of time when they’re properly restrained in a car seat that’s been installed with appropriate positioning.” However, using car safety seats for sleep in a non-traveling context does pose a risk to babies. So the American Academy of Pediatrics (AAP) recommends that babies who are still asleep when you have reached your destination should be transferred to a crib or bassinet.

But sometimes you *don’t* want them to fall asleep in the car.

That same baby sleep magic that brings relief after a long night of fussing can throw you into a panic during the afternoon when you are out running errands. When you notice that it’s too quiet and look back to see that little head tipped to the side, eyes closed, and that sweet little face drifting into slumber, you can feel desperate to keep your baby awake until you get home for a proper nap.

Here’s what you can do to keep your baby awake until you get out of the car:

• Make sure they are not overtired, which makes falling asleep almost a sure bet.
• Avoid car rides 30-45 minutes before naptime to preserve that window of opportunity when your baby will fall asleep easily for a scheduled nap.
• Skip the bottle or pacifier in the car seat because sucking is very soothing and will likely lead to drowsiness.
• Distract them to keep those eyes open.
• Pull over and take them out for a little fresh air and change of scenery.

Bottom Line: Being able to soothe a squalling baby with a car ride is a huge relief. But if a car ride results in an unwanted short power nap, don’t worry or stress and just remember that you can try to put your baby down again after they’ve been up awhile. Push that nap to later, just for today, mama.

Editor’s note: The American Academy of Pediatrics recommends against routine sleeping in sitting devices for infants. Here’s why pediatricians don’t want babies to sleep in car seats outside of the car.