Infant car seats have saved thousands of babies who otherwise would have died in traffic accidents, but a new study suggests that using the seats too much outside cars can be dangerous.

More than 8,700 infants end up in the emergency room each year because their car seats are used improperly outside the car, according to study presented Monday at the American Academy of Pediatrics’ annual meeting in Washington.[…]

Most of the injuries in [pediatric orthopedist Shital] Parikh’s study occurred when car seats fell off tables, countertops or other high surfaces. In some cases, babies who weren’t securely buckled fell out of the seats. Babies also were injured when car seats flipped over on soft surfaces, such as beds and couches, where infants can suffocate, he says.

Injury isn’t the only risk for babies who spend too much time in their car seats:

Physical therapists are seeing more babies with “container syndrome,” or weak muscles and flat heads caused by too much time spent lying on their backs, says Colleen Coulter-O’Berry of the American Physical Therapy Association.

And a study in Pediatrics in August found that car seats can make it difficult for babies to get enough oxygen, which led the authors to suggest that the seats be used only while infants are in cars.

If your baby falls asleep in your car or van, it’s fine to bring the car seat inside (as long as you place it in a safe place on the floor). But for the most part, car seats belong in motor vehicles. Wearing your baby in a soft carrier “meets a baby’s need for physical contact, comfort, security, stimulation and movement, all of which encourage neurological development.” Babywearing is also more comfortable for parents than lugging around a car seat or holding a baby in your arms for long periods. I wrote about my favorite types of baby carriers here.

A fantastic resource on the connections between touch, motion and brain development is What’s Going On In There?, a book by neurologist Lise Eliot.