Sudden Infant Death Syndrome (SIDS)

Sudden infant death syndrome (SIDS) is the death of a child under age 1 with no known cause — even after a full investigation.

While SIDS isn't uncommon, its cause can be hard to trace. The best prevention is understanding the best practices for your baby's sleeping environment.

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What Is SIDS?

Doctors define sudden infant death syndrome (SIDS) as the death of a baby under age 1 where the cause of death isn't obvious until after investigation.

Health care providers, police officers, and other officials investigate infant deaths to figure out their causes. According to the National Institutes of Health (NIH), this investigation includes a complete autopsy, examination of the death scene, and review of the baby’s clinical history.

If they cannot determine a cause of death or explain why the baby died, the medical examiner or coroner may classify the death as SIDS. Most cases of SIDS are unknown, but nearly 30% are a result of strangulation or suffocation in bed.

Crib death is an older term for SIDS that focused on the baby’s bed. As it became known that SIDS can occur in any sleeping area — such as bassinets, cribs, portable cribs/play yards, and U-shaped pillow bolsters – the term fell out of favor and is no longer is used.

How common is SIDS?

About 3,400 babies in the United States die suddenly and unexpectedly each year. According to the latest statistics from the CDC, in 2020, SIDS accounted for 41%, or nearly 1,400, of those deaths.

In addition:

Another 27% died of accidental suffocation or strangulation.
The remaining 32% died of another unknown cause.

What are the types of SIDS?

SIDS is one type of sudden unexpected infant death (SUID).

SUID is an umbrella term for all sudden, unexpected infant deaths – those from known causes, such as an injury, accident, or disease, and those from unknown causes.

Types of SUID are:

Sudden infant death syndrome (SIDS).
Unknown cause.
Accidental suffocation and strangulation in bed.

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What Causes SIDS?

Researchers don't know exactly what causes SIDS. Although scientists have found changes in the brains and genes of some babies who've died of SIDS, these issues alone are unlikely to cause death.

The National Institutes of Health (NIH) has a three-pronged theory for understanding how SIDS may happen.

Called the “Triple-Risk Model,” the theory suggests:

The baby has at least one unknown medical condition that parents and providers couldn't know about or test for. These include brain defects or genetic issues that affect heart rate or breathing.
The baby is in a critical period of development. Babies go through periods of fast growth and changes in blood pressure, breathing, sleeping patterns, and immunity. The baby’s body may be unstable and react in unexpected ways during these growth spurts.
An outside stressor is added to their sleep, such as being placed on their belly or being exposed to secondhand smoke in their sleeping environment.

Each situation by itself might not be a problem. Babies’ developing body systems usually can adjust to stresses and changes when just one or two risks are present. But when all three risks occur, a SIDS death becomes more likely.

One thing is certain, however – SIDS isn't a result of vaccines.

Infants are given several vaccines within the first six months of life. While this is also a common timeframe for SIDS to occur, it isn't linked to vaccinations.

Vaccines are rigorously tested before being given to the public, particularly infants. Despite the correlating time frame, no data has shown a link between any vaccination and SIDS.

What are SIDS risk factors?

Certain situations may increase the risk of SIDS and other sleep-related infant deaths, such as entrapment, strangulation, and suffocation.

Many risks are manageable – meaning that you can take action to lower your baby’s risk of SIDS.

The key risk factors for SIDS are:

Bed sharing/co-sleeping – Sharing a soft armchair, adult bed or waterbed, or couch with a baby can be very dangerous for your baby and raise the risk of SUID.
Birth-related factors – Low birthweight babies (weighing 5.8 pounds or less) are at higher risk for SIDS, as are preterm babies (born before 37 weeks of pregnancy).
Nutrition – Babies who are formula-fed are at higher risk of SIDS than babies who are breastfed. Getting human milk for any length of time is more protective against SIDS than getting no human milk at all.
Immunizations – Unvaccinated babies have a higher risk of SIDS than vaccinated babies.
Recent illness – Babies who have had a high fever within the past two to three weeks are at higher risk of SIDS.
Pregnancy factors – Babies are at higher risk of SIDS if their mothers delayed or skipped regular prenatal care throughout their pregnancy or smoked, drank alcohol, or used drugs while pregnant.
Race/ethnicity – Black/African American, Native American, and Native Alaskan babies are at higher risk for SIDS than White, Hispanic, and Asian/Pacific Islander infants.
Sleep position – Babies who are placed on their bellies or sides to sleep are at higher risk for SIDS. Babies who regularly sleep on their backs but who are placed on their stomachs or sides for sleep, such as for a nap, are at very high risk of SIDS.
Temperature – Overheated babies are at higher risk for SIDS. Babies are more likely to overheat when placed on their bellies to sleep. Over-bundling, or dressing a baby in too many layers of clothing and bedding for the temperature of the room, can increase the risk of SIDS.
Pacifiers during sleep – Babies who didn't sleep with a pacifier had a higher risk of SIDS than babies who sleep with pacifiers.
Sleep location – Babies who share a room (but not a bed) with their parents have a lower risk of SIDS than babies who sleep in their own rooms.

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How Can I Prevent SIDS?

While there may not be a direct cause for sudden infant death syndrome, the best way to prevent SIDS is to provide your infant with a proper sleeping area.

Here are some ways you can best prevent SIDS:

Always place your baby on their back to sleep.
Breastfeed your baby.
Do not smoke during your pregnancy or around your infant.
Keep unnecessary objects and loose bedding away from the sleeping area of your infant.
Keep the room your baby sleeps in at a comfortable temperature to prevent overheating. (Ideal: 68 to 72 degrees F.)
Sleep in the same room — but not the same bed — as your infant for the first six months.
Place your baby on a firm, level sleeping surface, like a crib mattress with a fitted sheet.

For additional resources, look to the Safe to Sleep campaign.

By UPMC Editorial Staff. Last reviewed on 2024-09-05.