Car seats are obviously meant to be used in the car, but in recent years the designs of modern infant car seats have made them so portable many parents keep babies in them even outside of the vehicle. Many parents arrive at a destination, take the whole car seat out and lug it inside so their babies can keep sleeping.

But now, the American Academy of Pediatrics is recommending against this after a new study published in the journal Pediatrics found that a significant number of infant deaths are occurring in car seats that aren’t being used in the car, but rather as a substitute for a crib or bassinet, especially when babies are in the care of a childcare provider.

Researchers investigated 11,779 infant sleep-related deaths over the course of a decade and found that 348 (3%) babies died in sitting devices, most of which (63%) were car seats that were not being used for their intended purpose. The remaining deaths happened in bouncers or swings (35%) and strollers (2%).

When the pediatricians looked into infant deaths that occurred in bouncers and swings, they learned most happened when the baby was at home with a parent. But they noted that when it comes to car seats, more babies were under the care of a childcare provider. “There are higher odds of sleep-related infant death in sitting devices when a child care provider or baby-sitter is the primary supervisor,” they wrote.

There have been several highly publicized cases of this in recent years. Ali Dodd lost her 11-week-old son Shepard in 2015 after he was put down for a nap in his infant car seat while at an in-home day care. It was only his sixth day in day care.

Dodd now advocates tirelessly for safe sleep and paid family leave in the hopes of preventing deaths like Shepard’s. She’s pleased to see the AAP drawing attention to data proving that sleeping in inclined sleepers and sitting devices is dangerous for babies. “The more this is talked about that more likely parents will accept this as fact. Babies should always be placed on their backs, alone in their crib or Pack N’ Play for every sleep time,” Dodd tells Motherly.

She continues: “If my son had been placed in a safe sleep environment I would likely still be watching him grow up. That’s a privilege I want for more American families.”

Parents, childcare providers, grandparents and anyone else who watches a baby should be aware that car seats are not a safe place for naps when used outside the car.

Children are going to fall asleep in their car seats while in a moving vehicle from time to time, and parents shouldn’t panic about that—the seats are made to be used in the car. As noted in a study The Journal of Pediatrics, 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.

The danger is when the seats are used on the floor, a table or a bed. Instead of letting a baby sleep in a car seat the American Academy of Pediatrics recommends babies nap and sleep “on a firm sleep surface such as a crib or bassinet with a tight-fitting sheet.” There should be no soft bedding, pillows, toys or bumpers in the crib.

Bottom line: Car seats save lives when used in the car, but they are absolutely not a replacement for a bassinet or a crib, and everyone who is taking care of babies should know this.

[A version of this post was originally published May 22, 2019.]