Sudden Infant Death Syndrome, or SIDS as it is commonly called, is a catch-all term for any baby who dies suddenly without there being a visible and apparent cause of death. More than 4,500 infants die suddenly each year from factors such as accidental suffocation and heart malfunction, properly referred to as Sudden Unexpected Infant Death. In roughly half of these cases the death can’t be explained, in which case they are classified as SIDS. SIDS is one of the leading causes of death for infants under a year of age. Doctors and scientists do not know precisely what it is or what causes it, though recent research is starting to point to some clues and a few different risk factors.

What causes SIDS?

The most recent work suggests that most SIDS cases may be due to suffocation or asphyxiation, likely caused by respiratory problems during sleep. Some scientists suspect pockets of carbon dioxide may suffocate a baby whose mouth is too close to an obstruction. Another recent study found that low levels of the hormone serotonin might be to blame and can increase the risk of SIDS. Serotonin regulates breathing, temperatures, sleeping, waking, and other automatic functions. It normally helps babies respond to high carbon-dioxide levels during sleep by prompting them to wake up and shift their head position to get fresh air. When placed face down, their exhaled carbon dioxide may pool in loose bedding and be breathed back in. Normally babies sense high carbon dioxide levels and will wake up. Yet babies who fail to respond appropriately may never wake up. The researchers found that serotonin levels were 26% lower in the postpartum tissue of SIDS babies – a good indication that low serotonin levels could play a role.

Risk factors for SIDS

1. The risk for SIDS peaks at around two months of age and then gradually drops. Fewer than 5% of SIDS deaths occur after 6 months. This is likely because as babies age they develop the necessary muscle strength to move their head around, which fits neatly into the asphyxiation theory of SIDS.

2. Boys are at a slightly higher risk factor than girls, with about 60% of SIDS victims being infant boys. A recent study published in the medical journal Sleep found that male infants between the ages of two to four weeks were more easily roused throughout the night than girls the same age. (This difference in sleep patterns disappears by two or three months of age.) As a result, parents may be tempted to calm an infant by putting him to sleep on his stomach, which increases the risk of SIDS.

SIDS Prevention: What parents can do to reduce the risk

Despite the lack of a solid understanding about SIDS, scientists have been able to tease out some hints about what causes it, which has led to some progress in preventing SIDS. The good news is that SIDS deaths have fallen by more than half since the American Academy of Pediatrics first began recommending that babies sleep on their backs rather than their stomachs. Here are some steps that parents should take to reduce the risk of SIDS:

1. Always put babies on their back to sleep, at least until they are closer to one year of age.

2. It’s believed that the use of a pacifier can reduce the risk for SIDS. Though doctors aren’t quite sure why, they suspect it helps keep the airway open. It also might strengthen muscles in the upper airway or prevent a baby from rolling onto their face. So it’s recommended that you allow a baby to fall asleep with their pacifier.

3. Keep your baby close but in a separate bed. Baby should sleep in their own crib or bassinet in the parent’s room, but never in the parent’s bed, at least not without a specialized bed bassinet designed precicly for that purpose. The American Academy of Pediatrics recommends that infants sleep in their parent’s room until they are at least 6 months old.

4. Use a firm crib mattress with a tight fitting sheet, and do not put loose blankets, pillows or other soft items in the crib until your baby gets older. Use a wearable blanket or sleep sack to keep your baby warm.

5. Use a fan to circulate the air in the room where your baby sleeps. A gentle breeze can dissipate any pockets of carbon dioxide that might form, thus reducing the risk of SIDS. It also helps by preventing your baby from overheating.

6. Breastfeed your baby. Again, although doctors aren’t quite sure why, breast-fed babies seem to have a lower incidence of SIDS.

7. Do not expose your baby to cigarette smoke, and never smoke in your house or car, even when the baby isn’t around. (Residual residue from cigarettes, known as third-hand smoke, comes to rest on different surfaces and can give off invisible toxins through interaction with air molecules for several weeks afterwards.) Not only can cigarette smoke cause respiratory problems, but the chemical compounds in cigarettes can affect your baby’s body in other ways.

8. Allow for lots of “tummy time” with your baby when they are awake to strengthen the muscles in their head and neck. Just don’t leave a baby unattended on their stomach.