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What causes SIDS?

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Health care providers and researchers don’t know the exact cause, but there are many theories.

More and more research evidence suggests that infants who die from SIDS are born with brain abnormalities or defects. These defects are typically found within a network of nerve cells that rely on a chemical called serotonin that allows one nerve cell to send a signal to another nerve cell. The cells are located in the part of the brain that probably controls breathing, heart rate, blood pressure, temperature, and waking from sleep.

But scientists believe that brain defects alone may not be enough to cause a SIDS death. Evidence suggests that other events must also occur for an infant to die from SIDS. Researchers use the Triple-Risk Model to explain this concept. In this model, all three factors have to occur for an infant to die from SIDS. Having only one of these factors may not be enough to cause death from SIDS, but when all three combine, the chances of SIDS are high.

These factors are:1,2,3

  • At-risk infant. An infant has an unknown problem—such as a genetic change or a brain defect—that puts him or her at risk for SIDS. Health care providers, parents, and caregivers don’t know about these problems, so they don’t know the infant is at risk.
  • Important time in infant’s development. During the first 6 months after birth, infants go through many quick phases of growth that can change how well the body controls or regulates itself. Also, infant’s bodies are learning how to respond to their environment.
  • Stressors in the environment. All infants have stressors in their environments—sometimes called external stressors because they are outside the body. Being placed to sleep on the stomach, overheating during sleep, and exposure to cigarette smoke are all examples of external stressors. Infants who have no problems like those explained above can usually correct or overcome external stressors to survive and thrive. But an infant who has an unknown problem and whose body systems are immature and unstable might not be able to overcome these stressors.

According to the Triple-Risk Theory, all three things have to be present for SIDS to occur.

Removing one of these factors—such as external stressors—may tip the balance in favor of the infant’s survival. Because the first two situations can’t be seen or pinpointed, the most effective way to reduce the risk of SIDS is to remove or reduce environmental stressors. Strategies to remove these stressors form the basis of the Safe to Sleep campaign messages.


  1. Moon, R. Y., Horne, R. S. C., Hauck, F. R. (2007). Sudden infant death syndrome. Lancet, 370, 1578-1587. [top]
  2. Paterson, D. S., et al. (2006). Multiple serotonergic brainstem abnormalities in Sudden Infant Death Syndrome. Journal of the American Medical Association, 296, 2124-2132. Retrieved June 15, 2012, from http://jama.jamanetwork.com/article.aspx?volume=296&issue=17&page=2124 External Web Site Policy [top]
  3. American Academy of Pediatrics. (2011). SIDS and other sleep-related infant deaths: Expansion of recommendations for a safe infant sleeping environment. Pediatrics, 128, 1030-1039. Retrieved June 15, 2012, from http://pediatrics.aappublications.org/content/early/2011/10/12/peds.2011-2284.full.pdf+html External Web Site Policy (PDF - 336 KB) [top]

Last Updated Date: 11/30/2012
Last Reviewed Date: 04/12/2013
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