Sudden Infant Death Syndrome (SIDS)

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Sudden infant death syndrome (SIDS) is the sudden, unexplained death of an apparently healthy child younger than one year of age. Researchers estimate that SIDS is the cause of about 2,500 infant deaths each year.


Other Names

  • Crib death
  • Cot death


  • It is the major cause of death in infants from one month to one year of age, with most deaths occurring between two and four months
  • It can occur in seemingly healthy infants
  • It often occurs during sleep and is without signs of suffering
  • It is a recognized medical disorder
  • It is not preventable, but the risk can be reduced by placing the baby on his or her back to sleep, providing a firm surface on which to sleep, minimizing the amount of blankets, pillows, and stuffed animals in the sleeping environment, making sure the household is smoke-free, and keeping the baby in cool temperatures
  • It is a separate cause of mortality from suffocation, child abuse, or neglect

Signs and Symptoms

SIDS has no warning signs or symptoms. Death is sudden, unexpected, and occurs in previously healthy infants.

  • It is not caused by vomiting, choking, or minor illnesses such as colds or infections
  • It is not caused by the diphtheria, pertussis, tetanus (DPT) vaccine or other immunizations
  • It is not the cause of every unexpected infant death
  • It is diagnosed only after an autopsy, examination of the death scene, and review of the infant's and family's clinical histories fail to reveal any other other cause
  • The infant's death can leave many unanswered questions, which may be a source of intense grief for parents and families


Certain changes are commonly noticed in SIDS babies during autopsy. These include petechial hemorrahges, pulmonary edema, evidence of chronic, low-grade asphyxia, and changes in the arcuate nucleus in the brain. Often there are no autopsy findings, and this alone can confirm the diagnosis of SIDS.

SIDS is a postmortem diagnosis. It is a diagnosis of exclusion, meaning that other explanations must be ruled out. If there is no other identifiable explanation and the autopsy finds no cause of death, SIDS is diagnosed.


Decades of research have failed to establish a clear-cut cause of death in SIDS, though many hypotheses have been suggested. Some recent theories include:

Triple risk model

This theory proposes that three factors are present in cases of SIDS:

  • A biological vulnerability, such as an unrecognized congenital heart or brain defect or metabolic deficiency
  • That the baby is in a critical developmental period (usually the first six months of life) and
  • External stressors, which are outside or environmental challenges that a normal baby can easily overcome and survive but an already vulnerable baby may not. Stressors such as exposure to second-hand smoke, tummy sleeping, or an upper respiratory infection alone do not cause death in healthy infants but could trigger a sudden, unexpected death in a vulnerable infant.[2]

Delayed brain development

A leading hypothesis is that SIDS may reflect a delay in the development of nerve cells and nuclei within the brain that are critical to normal heart and lung function. Examinations of the brainstems of infants given the diagnosis of SIDS have revealed a developmental delay in formation of a region of the brain known as the arcuate nucleus and related neural pathways of the brain. These pathways are thought to be crucial to regulating breathing and blood pressure responses. This developmental delay may impact the infant's ability to awaken and/or respond to a variety of physiological stimuli.

Abnormal lung development

Another theory is that abnormal lung development, potentially caused in some cases by the mother's smoking during pregnancy, combined with immature breathing circuitry in the brain causes the baby to stop breathing.[3]

Other theories

  • Child abuse is often examined in cases of SIDS. Child abuse can cause sudden, unexplained death in infancy, but most SIDS cases are not related to child abuse.[4]
  • There may be genetic factors involved in SIDS, though it is likely that other factors must be present in conjunction with genetics.[5]

Risk Factors

The following factors are not known to definitively cause SIDS, but their presence increases the risk that SIDS will happen. It may be that some other unidentified factor casues both SIDS and the risk factor.

Maternal risk factors

Risk factors in the mother include: [6]

  • Smoking during pregnancy and, to a lesser degree, after birth
  • Illegal drug use during pregnancy
  • Short interval between pregnancies
  • Urinary tract infection or other illness during pregnancy
  • Low socioeconomic status
  • Being unmarried
  • Having given birth twice or more already
  • Being less than twenty years old at first pregnancy
  • Decreased number of prenatal visits
  • Crowding in the home
  • Not completing high school
  • Anemia during pregnancy
  • Weight gain less than twenty pounds during pregnancy

Infant risk factors

  • Sleeping on the belly (prone) or on the side, especially when not accustomed to this position [7]
  • Intrauterine growth retardation
  • Prematurity
  • Exposure to passive smoking
  • Low birth weight
  • African American race: African-American babies are more than two times as likely to die of SIDS than Caucasian babies [8]
  • American Indian or Alaskan Native race: these babies are nearly three times as likely to die of SIDS as Caucasian babies
  • Male sex
  • Triplets
  • Cold weather months
  • Overheating
  • Parent sleeping with infant, especially if parents smoke[9]
  • Soft sleeping surface

Factors that do not appear to increase the risk of SIDS

No link has been found between SIDS and the following factors:

  • Maternal alcohol use
  • Recent vaccination
  • Sickle cell disease
  • Viral infections
  • Child abuse reports in the home


The following recommendations are based on factors that are known or strongly suspected to reduce the risk of SIDS. To learn more, read the American Academy of Pediatrics Task Force on SIDS recommendations [10]

  • The "Back to Sleep" campaign encourages parents to place babies on their backs to sleep. First launched in 1992 and further revised in 2000, it has dramatically reduced SIDS death rates in countries that have adopted the policy. Babies should be placed on their backs to sleep every time they sleep, including naps. Babies who usually sleep on their backs but who are then placed on their stomachs are at increased risk for SIDS. The campaign stresses that is important for babies to sleep on their backs all the time, every time.
  • Firm sleeping surface. Babies should be placed on firm sleeping surfaces, such as a safety-approved crib mattress covered with a tightly-fitted sheet. They should never be placed on a pillow, quilt, sheepskin, or other soft surface to sleep. Consumer Product Safety Commission or ASTM certification of the mattress is recommended.
  • Keeping soft objects, toys, and loose bedding out of the baby’s sleep area. Parents should not use pillows, blankets, quilts, sheepskins, or pillow-like bumpers in the baby’s sleep area. All items must be kept away from the baby’s face if included in the crib.
  • Ensuring the baby is not overheaded. The baby should be dressed in light sleep clothing (not overbundled in clothing or blankets) and the room kept at a temperature that is within the comfortable range for an adult.
  • Breastfeeding
  • Mother and baby sleeping in the same room though not the same bed.
  • Good prenatal care. Babies born prematurely, especially secondary to preventable risk factors, have a higher risk of SIDS. Pregnant women should avoid smoking or using drugs during pregnancy, as well.
  • Avoiding exposure to tobacco after the baby is born.
  • The caregiver may offer a clean, dry pacifier when placing the baby down to sleep but should not force the baby to take it. The pacifier should not be coated in any sweet solution or tooth decay may eventually result. Pacifiers that fall out should not be reinserted. Babies who are breastfed should wait util they are at least one month old or until they are accustomed to breastfeeding before using a pacifier.
  • Home monitoring systems do not appear to reduce the risk of SIDS.

Concerns about back-sleeping

Some parents are reluctant to put their babies on their backs to sleep because they worry that the soft head will develop a flat spot on the back. This is called positional plagiocephaly.

Generally, flat spots on a baby’s head disappear after a few months when the baby learns to sit up. There are other ways to reduce the chance that flat spots will develop on the baby’s head, such as:

  • Providing "tummy time" when the baby is awake and someone is watching. Tummy time not only helps prevent flat spots, but it also helps strengthen a baby’s head, neck, and shoulder muscles.
  • Changing the direction that the baby faces in the crib from week to week, so he or she is not always lying on the same part of the head.
  • Avoiding too much time in car seats, carriers, and bouncers and holding the baby upright often during the day.


According to the CDC,[11] more than 4500 infants die each year in the United States due to unexplained causes. Half of these deaths are attributed to SIDS. SIDS is the leading cause of death in children between one month and one year of age. Most SIDS deaths occur when babies are between two months and four months of age, and 90% occur in babies under six months of age.


Sleep expert James McKenna cowrote a review article[12] with Thomas McDade reviewing the evidence surrounding the topic of co-sleeping and concluded that roomsharing with breastfeeding mothers saves lives. However, controversy still exists over whether bedsharing or cosleeping increases or decreases the risk of SIDS. The American Association of Pediatrics (AAP) has adopted the policy that recommends a separate but proximate sleeping environment for parent and child.[13]


Prior to 1992, parents had been advised to put their babies to sleep on their stomachs (prone), although evidence had been available since at least 1970 that this practice was potentially harmful.[14] In the early part of this century, SIDS was blamed on mechanical suffocation. In the 1940s, a pathologist named Dr. Abramson in New York noticed that two-thirds of SIDS babies had been found sleeping prone, and this led to published recognition that prone sleeping led to "mechanical suffocation."[15] However, a pediatrician named P.V. Woolley disputed this by placing blankets over babies' faces and demonstrating that they did not suffocate, thus weakening the case for supine sleep.[16]. Textbooks, including Dr. Spock's child-care manuals, varied in their recommendations and did not consistently advocate back-sleeping until 1995.

Notable Experts

James McKenna, PhD, studies infant sleep, breastfeeding, and SIDS. He runs the University of Notre Dame Mother-Baby Behavioral Sleep Lab.

Public Health

The Eunice Kennedy Shriver National Institute of Child Health and Human Development, Maternal and Child Health Bureau, American Academy of Pediatrics, SIDS Alliance, and Association of SIDS and Infant Mortality Programs support the Back to Sleep campaign, named for its recommendation to place healthy babies on their backs to sleep. Placing babies on their backs to sleep reduces the risk of Sudden Infant Death Syndrome (SIDS), also known as "crib death." This campaign has been successful in promoting infant back sleeping to parents, family members, child care providers, health professionals, and all other caregivers of infants.

Related Videos

This video from the NIH features Dr. Marian Willinger of the National Institute of Child Health and Human Development providing the latest information on Sudden Infant Death Syndrome (SIDS).

Video at YouTube


  1. Hunt CE, Hauck FR. Sudden infant death syndrome. In: Kliegman RM, Behrman RE, Jenson HB. Nelson Textbook of Pediatrics. 18th ed. Philadelphia PA: W.B. Saunders; 2007:1736-1742.
  2. Guntheroth W, Spiers P. The Triple Risk Hypotheses in Sudden Infant Death Syndrome. Pediatrics. 2002;110(5):e64. Full Text
  3. Ueda Y, Stick SM, Hall G, Sly PD. Control of breathing in infants born to smoking mothers. The Journal of Pediatrics. 1999;135(2 Pt 1):226-32. Abstract
  4. American Academy of Pediatrics. Distinguishing sudden infant death syndrome from child abuse fatalities. Pediatrics. 2001;107(2):437-41. Erratum in: Pediatrics 2001;108(2):512. Pediatrics 2001 Sep;108(3):812. Full Text
  5. Weese-Mayer DE, Ackerman MJ, Marazita ML, Berry-Kravis EM. Sudden Infant Death Syndrome: review of implicated genetic factors. American Journal of Medical Genetics, Part A. 2007;143(8):771-88. Abstract
  6. Getahun D, Amre D, Rhoads GG, Demissee K. Maternal and obstetric risk factors for sudden infant death syndrome in the United States. Obstetrics and Gynecology. 2004;103(4):646-52. Abstract
  7. Mitchell EA, Thach BT, Thompson JM, Williams S. Changing infants' sleep position increases risk of sudden infant death syndrome. New Zealand Cot Death Study. Arch Pediatr Adolesc Med.1999 ;153 :1136 –1141. Full Text
  8. Mathews TJ, Menacker F, MacDorman MF; Centers for Disease Control and Prevention, National Center for Health Statistics. Infant mortality statistics from the 2002 period: linked birth/infant death data set. Natl Vital Stat Rep. 2004;53(10):1-29. Abstract
  9. Horsley T, Clifford T, Barrowman N, Bennett S, Yazdi F, Sampson M, Moher D, Dingwall O, Schachter H, Côté A. Benefits and harms associated with the practice of bed sharing: a systematic review. Arch Pediatr Adolesc Med. 2007;161(3):237-45. Full Text
  10. American Academy of Pediatrics Task Force on Sudden Infant Death Syndrome. The changing concept of sudden infant death syndrome: diagnostic coding shifts, controversies regarding the sleeping environment, and new variables to consider in reducing risk. Pediatrics. 2005 Nov;116(5):1245-55. Epub 2005 Oct 10. Full Text
  11. Centers for Disease Control and Prevention. Sudden Infant Death Syndrome (SIDS)
  12. McKenna J, McDade T. Why babies should never sleep alone: A review of the co-sleeping controversy in relation to SIDS, bedsharing and breast feeding. Paediatric Respiratory Reviews. 2005; 6: 134-152. PDF
  13. American Academy of Pediatrics Task Force on Sudden Infant Death Syndrome. The changing concept of sudden infant death syndrome: diagnostic coding shifts, controversies regarding the sleeping environment, and new variables to consider in reducing risk. Pediatrics. 2005 Nov;116(5):1245-55. Epub 2005 Oct 10. Full Text
  14. Gilbert R, Salanti G, Harden M, See S. Infant sleeping position and the sudden infant death syndrome: systematic review of observational studies and historical review of recommendations from 1940 to 2002. Int J Epidemiol. 2005 Aug;34(4):874-87. Epub 2005 Apr 20. Full Text
  15. New York State Department of Health. Merchanical suffocation: leading cause of accidental death in early infancy. Health News 1945;22:33–34.
  16. Woolley PV. Mechanical suffocation during infancy. A comment on its relation to the total problem of sudden death. The Journal of Pediatrics 1945;26:572–75

External Links

Back to Sleep Campaign

The University of Notre Dame Mother-Baby Behavioral Sleep Lab

Centers for Disease Control and Prevention: What is SIDS?

Sudden Infant Death Syndrome (SIDS): Risk Factors

American SIDS Institute

SIDS Network

National Sudden Infant Death Resource Center (NSIDRC): What is SIDS?

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