Women’s Health discusses sudden infant death syndrome (SIDS) and what mothers need to know.

Unfortunately, no one is exactly sure how SIDS occurs, says Eileen Everly, M.D., a pediatrician at Children’s Hospital of Philadelphia, CHOP Karabots Pediatric Care Center. The key part of SIDS is the fact that a baby’s death is unexplained, even after investigation and the ruling out of other illnesses that can mimic SIDS, she says.

Some factors may put a baby at a higher risk of SIDS than others, such as brain defects, low birth weight, or a respiratory infection, the Mayo Clinic says. However, sleep environment is also a huge factor, which is why there’s been so much focus around safe sleep habits for babies.