Causes

A combination of physical and sleep environmental factors can make an infant more vulnerable to SIDS. These factors vary from child to child.

Physical factors

Physical factors associated with SIDS include:

• Brain defects. Some infants are born with problems that make them more likely to die of SIDS. In many of these babies, the portion of the brain that controls breathing and arousal from sleep hasn't matured enough to work properly.
• Low birth weight. Premature birth or being part of a multiple birth increases the likelihood that a baby's brain hasn't matured completely, so he or she has less control over such automatic processes as breathing and heart rate.
• Respiratory infection. Many infants who died of SIDS had recently had a cold, which might contribute to breathing problems.

Sleep environmental factors

The items in a baby's crib and his or her sleeping position can combine with a baby's physical problems to increase the risk of SIDS. Examples include:

• Sleeping on the stomach or side. Babies placed in these positions to sleep might have more difficulty breathing than those placed on their backs.
• Sleeping on a soft surface. Lying face down on a fluffy comforter, a soft mattress or a waterbed can block an infant's airway.
• Sharing a bed. While the risk of SIDS is lowered if an infant sleeps in the same room as his or her parents, the risk increases if the baby sleeps in the same bed with parents, siblings or pets.
• Overheating. Being too warm while sleeping can increase a baby's risk of SIDS.