Sudden Infant Death Syndrome (SIDS)

Sudden infant death syndrome (also known as SIDS, and sometimes called crib death) refers to the sudden death of an apparently healthy infant under one year of age whose death cannot be explained even after a complete investigation. SIDS is a subcategory of Sudden Unexpected Infant Death (SUID), which includes SIDS, unknown causes, and accidental suffocation and strangulation in bed.

Taking Care

Mrs. Wyatt is following all the instructions her doctor gave for the care of her new baby. She puts him to sleep both at night and for daytime naps on his back instead of on his stomach. She makes sure that the crib has a firm mattress and that no blankets, pillows, or toys are around the baby. She refrains from bundling her baby in thick clothing before putting the baby to bed.

The doctor recommended these precautions because they reduce the risk of sudden infant death syndrome (SIDS), a mysterious disorder that is a leading cause of death for children between the ages of one month and one year.

Since mothers like Mrs. Wyatt started to put their babies to sleep on their backs and began to adopt other preventive strategies, the number of SIDS deaths has dropped substantially. However, SIDS still accounts for about 1,500 deaths per year in the United States, usually while the babies are asleep in their cribs. No one knows for certain why these babies die. Most appear to be healthy until their deaths. Parents often feel guilt mixed with their grief over the death of their baby. They think perhaps they could have done something more for the baby, but SIDS is no one's fault.

What is Sudden Unexpected Infant Death (SUID)?

According to the Centers for Disease Control and Prevention, about 3,500 infants in the United States die suddenly and unexpectedly each year. Many people think of these deaths as the result of Sudden Infant Death Syndrome (SIDS), but that term is actually a subset of Sudden Unexpected Infant Death (SUID). The term is applied to infant deaths that remain unexplained even after a thorough autopsy and detailed investigation. Though the cause of death can't be explained, many occur while the infant is sleeping in an unsafe sleeping environment. Most often, no one sees these deaths and there are no tests to identify SIDS apart from deaths by suffocation.

Trends in Sudden Unexpected Infant Death (SUID) and Sudden Infant Death Syndrome (SIDS) by Cause in the United States, 1990–2013

Trends in Sudden Unexpected Infant Death (SUID) and Sudden Infant Death Syndrome (SIDS) by Cause in the United States, 1990–2013
SOURCE: 2013 Centers for Disease Control and Prevention (CDC), National Center for Health Statistics (NCHS), and National Vital Statistics System, Compressed Mortality File. “Sudden Unexpected Infant Death and Sudden Infant Death Syndrome.” Available online at: (accessed July 13, 2016). Table by Lumina Datamatics Ltd. © 2016 Cengage Learning®.

For some the term SIDS is inadequate since it excludes deaths by suffocation. SUID is a broader category, including accidental suffocation or strangulation in bed, unknown cases in which the cause of death could not be determined and an investigation was not conducted, as well as SIDS.

What Is Sudden Infant Death Syndrome?

SIDS is defined as the sudden death of an infant under one year of age, when no other cause of death is found after conducting an autopsy * , an investigation of the place where the baby died, and a review of the baby's medical history. However, even after a thorough investigation, it is hard to tell SIDS apart from other sleep-related infant deaths because no autopsy tests can tell for certain whether suffocation was the cause of death.

As a result, it can seem easier to describe SIDS by what it is not than what it is. SIDS does not result from suffocation, overlay (when another person rolls on top of or up against the infant while sleeping), choking, vomiting, or a fatal reaction to a vaccination * .

Researchers have explored the possible causes of SIDS for years, and many have come to believe that it results from a problem in an area of the brain that controls two important functions while infants are asleep: breathing and waking up. In 2006, a research team conducted autopsies on 31 infants who had died of SIDS, and they found that about three-fourths of the infants had abnormalities in a certain brain chemical called serotonin. The researchers believed the abnormality prevented the infants from responding normally when they were not getting enough oxygen. These responses include turning the head or taking deeper breaths. It was hoped that this finding would lead to tests that could help determine whether an infant actually died of SIDS and possibly to medications that might someday identify and prevent the problem.

Several factors can cause a baby to get insufficient oxygen. For example, babies might not get enough oxygen when they breathe air that is trapped in soft beds or in folds of blankets near their mouths. In such circumstances, they are breathing in their own exhaled carbon dioxide rather than the oxygen available in the air. A normal baby's brain gets the warning about the insufficient oxygen, but a baby with the serotonin abnormality does not.

A baby can also experience breathing difficulties from respiratory infections such as a cold or other ailment. This fact might explain why SIDS is more likely to occur in the winter, when the risk of infection is higher and when babies are more likely to be sleeping with extra bedclothes or blankets.

Researchers have investigated other possible physical problems that could contribute to the risk of SIDS. One possible factor is an immune system * disorder that creates too many white blood cells and proteins, which disrupt the brain's control over breathing and heart rate.

For decades, parents thought it was best to put babies to sleep on their stomachs. They assumed that if babies were on their backs, they might choke on their vomit if they threw up.

Doctors later explained that there was no reason to fear this potential for choking. In 1992, the American Academy of Pediatrics recommended that babies sleep on their backs, and in 1994, the National Institute of Child Health and Human Development and other organizations reiterated that call by launching a national Back to Sleep Campaign to reduce the risk of SIDS. Between 1992 and 1997, the number of children sleeping on their stomachs decreased dramatically, and the death rate from SIDS dropped by 50 percent.

The National Institute of Child Health and Human Development offers a number of ways to lower the risk of SIDS. These include:

Not all babies should sleep on their backs. A few have problems with their airways or with keeping food down. In these rare cases, parents should consult a doctor, who may recommend that the babies be placed on their stomachs on a firm mattress without soft pillows, blankets, or plush toys.

Some parents have misunderstood the intent of the Back to Sleep Campaign. They never put their children on their stomachs, even when they are awake. Doctors say it is important for children's physical and mental development to spend some time on their stomachs while they are awake, as long as an adult is watching.

SIDS is probably caused by a combination of factors, including those yet to be identified.

Who Is at Risk of Sudden Infant Death Syndrome?

SIDS can happen any time within the first year, but it occurs most often between the second and fourth month after birth. It seldom occurs during the first two weeks following birth or after six months. The vast majority of babies do not experience SIDS, even if they sleep on their stomachs, have infections, or sleep with blankets in their cribs. Others who sleep on their backs in ideal conditions still die of SIDS. No warning signs of SIDS are evident before a baby dies. Doctors only diagnose it after ruling out other possible causes of death.

In the United States, SIDS affects African American and Native American infants at least twice as often as Caucasians. Lack of worldwide documentation and investigation of infant deaths affects the validity of statistics for SIDS worldwide. In developed countries where deaths are tracked nationally, rates of SIDS vary widely, from one in 1,000 children to one in 10,000. Worldwide, SIDS was officially determined to be responsible for about 15,000 deaths in 2013.

Although research is beginning to suggest causes for SIDS, in 2016 no test was yet available to predict who would die of the disorder.

What Are the Risk Factors for Sudden Infant Death Syndrome?

A baby is more likely to die of SIDS if the baby has:

In addition, babies who are strictly bottle-fed have a higher risk of SIDS. One possible reason is that breastfeeding helps reduce the risk of the types of infections that may contribute to breathing problems.

See also Infection • Prematurity • Tobacco-Related Diseases: Overview


Books and Articles

Powell, Kendall. “SIDS Rate Has Declined, but 2,300 U.S. Babies Still Die Annually.” Washington Post, August 5, 2013. Available at: (accessed July 13, 2016).


Centers for Disease Control and Prevention. “Sudden Unexpected Infant Death and Sudden Infant Death Syndrome.” (accessed July 13, 2016).

Eunice Kennedy Shriver National Institute of Child Health and Human Development. “Sudden Infant Death Syndrome (SIDS) and Other Sleep-Related Causes of Infant Death.” (accessed July 13, 2016).


American Academy of Pediatrics. 141 Northwest Point Blvd., Elk Grove Village, IL 60007-1098. Toll-free: 800-433-9016. Website: (accessed July 13, 2016).

Association of Maternal and Child Health Programs. 2030 M St. NW, Suite 350, Washington, DC 20036. Telephone: 202-775-0436. Website: (accessed July 13, 2016).

Children's Safety Network. 43 Foundry Ave., Waltham, MA 024538313. Telephone: 617-618-2918. Website: (accessed July 13, 2016).

First Candle. 9 Newport Dr., Suite 200, Forest Hill, MD 21050. Telephone: 443-640-1049. Website: (accessed July 13, 2016).

Sudden Infant Death Syndrome Network, Inc. PO Box 520, Ledyard, CT 06339. Website: (accessed July 13, 2016).

* autopsy (AW-top-see) is an examination of a body after death to look for the cause of death or the effects of a disease.

* vaccination (vak-sih-NAY-shun), also called immunization, is giving, usually by an injection, a preparation of killed or weakened germs, or a part of a germ or product it produces, to prevent or lessen the severity of the disease caused by that germ.

* immune system (im-YOON) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.

  This information is not a tool for self-diagnosis or a substitute for professional care.