In the United States, about 3,700 infants die suddenly and unexpectedly each year. The combined rate of sudden unexpected infant death (SUID), which includes SIDS, accidental suffocation in bed, and deaths from unknown causes, was 100.9 per 100,000 live births in 2022. Of those deaths, SIDS specifically accounted for 41.7 per 100,000, making it the single largest category.
How SUID Deaths Break Down by Cause
SUID is an umbrella term covering three categories of sudden infant death. In 2022, the breakdown per 100,000 live births looked like this:
- SIDS (sudden infant death syndrome): 41.7
- Unknown cause: 30.8
- Accidental suffocation and strangulation in bed: 28.4
SIDS is diagnosed when no cause of death can be found after a thorough investigation, autopsy, and review of the infant’s medical history. The distinction between SIDS and “unknown cause” often depends on how thoroughly the death scene was investigated, which means some deaths classified as unknown cause may functionally be SIDS. This makes the true SIDS rate difficult to pin down precisely.
How Rates Have Changed Over Time
The SIDS rate in the U.S. dropped by more than 50% after the 1994 Back to Sleep campaign, which urged parents to place infants on their backs to sleep. In high-income North America, SIDS mortality fell from about 118 per 100,000 in 1991 to roughly 30 per 100,000 in 2021. That progress, however, has plateaued. The rate has held relatively steady for the past two decades, and SIDS remains the leading cause of death among infants between one month and one year old.
Globally, the 2021 SIDS mortality rate was about 24 per 100,000 live births, though this varies enormously by country. The U.S. rate of roughly 32 per 100,000 is higher than the global average, sitting alongside New Zealand (about 36 per 100,000) as an outlier among wealthy nations.
When SIDS Is Most Likely to Happen
About 95% of SIDS cases occur in the first six months of life. The highest-risk window is between two and four months of age. SIDS is rare after one year and almost unheard of after 12 months. This age pattern is one of the defining features of the syndrome and is consistent across countries and populations.
Racial and Ethnic Disparities
The gaps between racial and ethnic groups are stark, and in some cases they are getting worse. CDC data from 2017 to 2022 shows SUID rates per 100,000 live births vary dramatically:
- Non-Hispanic Black infants: 192.4 in 2017, rising to 244.0 in 2022
- American Indian or Alaska Native infants: 230.3 in 2017, relatively stable at 229.4 in 2022
- Native Hawaiian or Other Pacific Islander infants: 137.9 in 2017, rising to 237.1 in 2022
- Non-Hispanic White infants: 85.7 in 2017, roughly stable at 83.2 in 2022
- Hispanic infants: 56.0 in 2017, slightly higher at 61.6 in 2022
- Non-Hispanic Asian infants: 18.5 in 2017, rising to 31.5 in 2022
Black infants in 2022 died at nearly three times the rate of White infants, and American Indian or Alaska Native infants died at close to the same elevated rate. These disparities reflect systemic differences in access to safe sleep environments, prenatal care, housing stability, and exposure to environmental stressors like tobacco smoke, not biological differences between races.
Sleep Position and SIDS Risk
Placing a baby face-down to sleep is the single most well-documented risk factor. Across multiple large studies, stomach sleeping carries roughly 6 to 7 times the odds of SIDS compared to back sleeping. One study found the relative risk as high as 10.5 when comparing prone to supine positions. Side sleeping is safer than stomach sleeping but still carries more risk than back sleeping. The back-sleep recommendation is the foundation of every major safe sleep guideline, and the dramatic decline in SIDS rates since the 1990s is largely attributed to this one change in behavior.
Smoking and Secondhand Smoke
Tobacco exposure, both before and after birth, is one of the strongest modifiable risk factors. Mothers who smoked during pregnancy had nearly four times the odds of a SIDS death compared to non-smoking mothers. Postnatal smoking by the mother roughly doubled the risk. Even secondhand smoke exposure during pregnancy, meaning the mother lived with or spent time around other smokers, was associated with a fourfold increase in odds. The relationship between smoking and SIDS appears to be dose-dependent: the more cigarettes and the longer the exposure, the higher the risk.
Bed Sharing and Alcohol Use
Bed sharing is a nuanced risk factor. Sharing a bed with an infant becomes significantly more dangerous when combined with smoking, alcohol, or drug use. When parents smoke, the risk associated with bed sharing multiplies well beyond what either factor contributes alone. Alcohol consumption by the parent sharing the bed further amplifies that risk. For infants under three months, the combined risk multipliers exceed five times the baseline, even in some lower-risk scenarios. Sleeping with a baby on a sofa or armchair is dangerous in all circumstances, regardless of other factors.
Breastfeeding as a Protective Factor
Breastfeeding reduces the risk of SIDS by approximately 50% at all ages throughout infancy. Exclusive breastfeeding for at least one month cuts the risk in half. Even partial breastfeeding appears protective, though the evidence is stronger for exclusive breastfeeding. The protective effect likely comes from a combination of factors: breastfed infants tend to wake more easily, have stronger immune responses, and sleep in lighter stages, all of which may help during a moment of physiological stress. Current guidance recommends breastfeeding through at least six months as part of SIDS risk reduction.
Why the Rate Has Stopped Falling
The plateau in SIDS rates since the early 2000s is a source of frustration for researchers and public health officials. The easy gains from the back-sleep message have been realized. What remains are the harder problems: persistent racial disparities driven by structural inequality, continued tobacco and substance use during pregnancy, unsafe sleep environments tied to poverty and overcrowded housing, and incomplete understanding of the underlying biological mechanisms that make some infants vulnerable. Accidental suffocation deaths in bed have actually increased over this same period, partially offsetting the gains in SIDS-specific deaths and keeping the overall SUID rate stubbornly flat.