Baby boxes aren’t as safe as we once thought.

Originating in Finland in the 1930s, cardboard boxes filled with newborn essentials and a mattress have been touted as a better way to decrease your baby’s odds of SIDS (Sudden Infant Death Syndrome). Combined with Finland’s low SIDS rate (two deaths per 1,000 live births), the assumption that baby boxes decrease the risk of SIDS isn’t a scientific fact.

According to the British Medical Journal, using baby boxes as a regular place for baby to sleep can be dangerous. There are no safety regulations and boxes can be flammable and flimsy, plus it’s harder to see baby thanks to the high sides of the boxes. If left on the floor, pets and sibling have easier access to baby, too. In addition, there’s no correlation between the boxes and a decrease in infant mortality rates.

New Jersey was the first state in the US to send mothers home with baby boxes. And while their popularity has skyrocketed across the globe, boxes should only be used if nothing else is available for baby to sleep in. If you’re planning on using a baby box, The Lullaby Trust has some pointers.