Scientists still aren't sure exactly what causes Sudden Infant Death Syndrome, or SIDS, but some new research suggests better ventilation in a baby's sleeping area can reduce the risk of this mysterious and lethal respiratory failure.

Over the past two decades, the number of SIDS deaths in the United States and Europe has dropped dramatically. This came after researchers discovered that babies were less likely to die when they were placed on their backs to sleep.

One of the many researchers studying SIDS is Dr. De-Kun Li from the Kaiser Permanente medical system in California. He says scientists think SIDS may be caused when babies rebreathe, or breathe back in, the carbon dioxide that they've just exhaled.

"For example, sleeping on the back decreases the chance of rebreathing," Li says. "On the other hand, sleeping on the stomach increases chances of rebreathing. You put a baby on the soft bed, you increase the chance of rebreathing."

Li also says that using a pacifier can decrease the chance of rebreathing because a bulky pacifier keeps blankets from laying on a baby's face, thus preventing the baby from rebreathing carbon dioxide trapped under the blankets.

Li interviewed the parents of babies who had died of SIDS. Then he interviewed the parents of babies who had not died. He says he's found one important difference in the sleeping environment of children who lived: many had fans in the rooms where they were sleeping.

"If there was a fan in the infant's room, the infant's risk of SIDS was reduced by 72 percent compared to infant who did not have a fan of the room," Li says. 

The theory is that some babies have a subtle problem in their brains. These babies don't react when they rebreathe an excess of carbon dioxide. Usually this would provoke the baby to cough or move.

This is why fans become important.

"The fan can help dissipate any trapped carbon dioxide around the mouth or the baby's airway," Li says.

He says the practice of placing a fan in a baby's room should be added to the list of things parents can do to reduce the SIDS risk to their infants.  His research is published in the Archives of Pediatric and Adolescent Medicine.