[5] SIDS remains the leading cause of infant mortality in Western countries, constituting half of all post-neonatal deaths.

[1] Other measures include a firm mattress separate from but close to caregivers, no loose bedding, a relatively cool sleeping environment, using a pacifier, and avoiding exposure to tobacco smoke.

[16] SIDS is a diagnosis of exclusion and should be applied to only those cases in which an infant's death is sudden and unexpected, and remains unexplained after the performance of an adequate postmortem investigation, including: After investigation, some of these infant deaths are found to be caused by suffocation, hyperthermia or hypothermia, neglect or some other defined cause.

[7] Although studies have identified risk factors for SIDS, such as putting infants to bed on their bellies, there has been little understanding of the syndrome's biological process or its potential causes.

[20] The frequency of SIDS does appear to be influenced by social, economic, or cultural factors, such as maternal education, race or ethnicity, or poverty.

[21] SIDS is believed to occur when an infant with an underlying biological vulnerability, who is at a critical development age, is exposed to an external trigger.

[3] The following risk factors generally contribute either to the underlying biological vulnerability or represent an external trigger: SIDS rates are higher in babies of mothers who smoke during pregnancy.

[31] The American Academy of Pediatrics thus recommends "room-sharing without bed-sharing", stating that such an arrangement can decrease the risk of SIDS by up to 50%.

Note that when multiracial parentage is involved, infant race is arbitrarily assigned to one category or the other; most often it is chosen by the mother.

About 10 to 20% of SIDS cases are believed to be due to channelopathies, which are inherited defects in the ion channels which play an important role in the contraction of the heart.

[48] A 2022 study found that infants who died of SIDS exhibited significantly lower specific activity of butyrylcholinesterase, an enzyme involved in the brain's arousal pathway, shortly after birth.

This can serve as a biomarker to identify infants with a potential autonomic cholinergic dysfunction and elevated risk for SIDS.

[52] Premature babies are at four times the risk of SIDS, possibly related to an underdeveloped ability to automatically control the cardiovascular system.

[53] A 2-part edition of The Cook Report from 1994 claimed that antimony- and phosphorus-containing compounds used as fire retardants in PVC and other cot mattress materials were a cause of SIDS.

Subsequent investigation by an Expert Panel led by Lady Limerick found that there was no evidence to support this claim.

Genes indicating susceptibility to MCAD and Long QT syndrome do not protect an infant from dying of classical SIDS.

The study found that 69% of autopsies listed other possible risk factors that could have led to death, such as unsafe bedding or sleeping with adults.

[64][65] Since an autopsy is often unable to determine whether asphyxiation is caused intentionally, medical practitioners rely on patient and family history and evidence of prior abuse to identify cases of infanticide.

[9] Some estimates in the 1980s and 1990s placed the potential rate of SIDS deaths caused by maltreatment around 10% and as high as 40%, but data from interventions such as the Safe to Sleep campaign suggests that these figures were substantially inflated.

[9] Some have underestimated the risk of two SIDS deaths occurring in the same family; the Royal Statistical Society issued a media release refuting expert testimony in one UK case, in which the conviction was subsequently overturned.

[66] A number of measures have been found to be effective in preventing SIDS, including changing the sleeping position to supine, breastfeeding, limiting soft bedding, immunizing the infant and using pacifiers.

[11] A 2016 review found tentative evidence that swaddling increases the risk of SIDS, especially among babies placed on their bellies or sides while sleeping.

[70] It is thus recommended by the American Academy of Pediatrics and promoted as a best practice by the US National Institute of Child Health and Human Development (NICHD) "Safe to Sleep" campaign.

"[73] Due to the obvious dangers, experts have also warned that blankets or other clothing not be placed over a baby's head.

[87] Rates are calculated per 100,000 live births to enable more accurate comparison across groups of different total population size.

More than 50% of African American infants were placed in non-recommended sleeping positions, according to a 2012 study completed in South Carolina,[88] indicating that cultural factors can be protective as well as problematic.

[89] The rate of SIDS per 1000 births varies among ethnic groups in the United States:[28][90] Many popular media portrayals of infants show them in non-recommended sleeping positions.