Sudden Infant Death Syndrome (SIDS)

  • Medical Author: Patrick L. Carolan, MD
  • Medical Editor: David Perlstein, MD, MBA, FAAP
    David Perlstein, MD, MBA, FAAP

    David Perlstein, MD, MBA, FAAP

    Dr. Perlstein received his Medical Degree from the University of Cincinnati and then completed his internship and residency in pediatrics at The New York Hospital, Cornell medical Center in New York City. After serving an additional year as Chief Pediatric Resident, he worked as a private practitioner and then was appointed Director of Ambulatory Pediatrics at St. Barnabas Hospital in the Bronx.

Sudden infant death syndrome (SIDS) facts

  • Sudden infant death syndrome is defined as the sudden, unexpected death of an infant younger than 1 year of age.
  • It typically occurs associated with a period of sleep.
  • SIDS is rare during the first month of life. Risk peaks in infants 2-4 months of age and then declines.
  • SIDS is diagnosed once all recognizable causes of infant death have been ruled out, including infection, trauma, or a condition related to the heart, lungs, or central nervous system.
  • SIDS risk can be reduced by following the guidelines of the "Safe to Sleep" campaign, including placing an infant to sleep on his/her back and avoiding objects within the sleep space that may interfere with normal breathing.

What is sudden infant death syndrome (SIDS)?

Sudden infant death syndrome (also known as SIDS) is defined as the sudden, unexpected death of an infant younger than 1 year of age. If the child's death remains unexplained after a formal investigation into the circumstances of the death (including performance of a complete autopsy, examination of the death scene, and review of the clinical history), the death is then attributed to SIDS. Sudden infant death is a tragic event for any parent or caregiver.

  • SIDS is suspected when a previously healthy infant, usually younger than 6 months of age, is found dead following a period of sleep. In most cases, no sign of distress is identifiable. The baby typically feeds normally prior to going to sleep. The infant is then discovered lifeless, without pulse or respiration. Cardiopulmonary resuscitation (CPR) may be initiated at the scene, but evidence shows a lack of beneficial effect from CPR. The cause of death remains unknown despite a careful review of the medical history, scene investigation, and autopsy.
    • SIDS is rare during the first month of life. Risk peaks in infants 2-4 months of age and then declines.
    • About 90% of SIDS deaths occur in infants younger than 6 months of age.

What is the cause of SIDS?

The cause (or causes) of SIDS is still unknown. Despite the dramatic decrease in the occurrence of SIDS in the United States and worldwide in recent years, SIDS remains one of the leading causes of death during infancy beyond the first 30 days following birth. It is generally accepted that SIDS may be the result of multiple interacting factors.

  • Infant development: A leading hypothesis is that SIDS may reflect a delay or abnormality in the development of nerve cells within the brain that are critical to normal heart and lung function. Research examinations of the brainstems of infants who died with a diagnosis of SIDS have revealed a developmental delay in the formation and function of several serotonin-binding nerve cell pathways within the brain. These pathways are thought to be crucial to regulating breathing, heart rate, and blood pressure responses during awakening from sleep.
    • The hypothesis is that certain infants, for reasons yet to be determined, may experience abnormal or delayed development of specific critical areas of their brain. This could negatively affect the function and connectivity to regions regulating arousal during sleep.
    • Arousal, in this context, refers to an infant's ability to awaken and/or respond to a variety of physiological stimuli. For example, a child sleeping facedown (prone) may move his or her face into such a position so that the nose and mouth are completely obstructed. This may alter the levels of oxygen or carbon dioxide in the infant's blood. Normally, these changes would trigger arousal responses, prompting the infant to move his or her head to the side to relieve this obstruction.
    • Other protective responses to stressful stimuli may be defective in infants who are vulnerable to SIDS. One such reflex is the laryngeal chemoreflex which arises from nerve cell pathways located in the back of the throat (pharynx) and within the voice box (larynx) and upper airway. This reflex regulates changes in breathing, heart rate, and blood pressure when portions of the airway are stimulated by fluids like saliva or regurgitated stomach contents. Having saliva in the airway may activate this reflex, triggering swallowing responses which help to keep the airway clear. When an infant is in the facedown position, the rate of swallowing is decreased. Protective arousal responses to these laryngeal reflexes are also diminished in active sleep when infants are in the facedown sleep position.

  • Rebreathing stresses: When a baby is facedown, air movement around the mouth may be impaired. This can cause the baby to re-breathe carbon dioxide that the baby has just exhaled. Soft bedding and gas-trapping objects, such as blankets, comforters, waterbeds, and soft mattresses, as well as stuffed or plush toys are other types of sleep surfaces that may impair normal air movement around the baby's mouth and nose when positioned facedown.
  • Hyperthermia (increased temperature): Overdressing, using excessive coverings, or increasing the air temperature may lead to an increased metabolic rate in these infants and eventual loss of breathing control. However, it is unclear whether the increased temperature is an independent factor or if it is just a reflection of the use of more clothing or blankets that may act as objects obstructing the airway.

Even though the specific cause (or causes) of SIDS remains unknown, scientific efforts have eliminated several previously held theories. We now know the following about SIDS:

  • Apnea is a term that describes the clinical situation in which a person's breathing stops spontaneously. Apnea associated with prematurity and apnea which occurs during infancy are felt to be clinical conditions that are distinct from SIDS. Infants with apnea may, in some cases, be managed with electronic monitors prescribed by doctors that track heart rate and respiratory activity. Apnea monitors will not prevent SIDS.
  • SIDS is neither predictable nor preventable.
  • Infants may experience episodes termed apparent life-threatening events (ALTE). These are clinical events in which young infants may experience abrupt changes in breathing, color, or muscle tone. Common causes of ALTE include viral respiratory infections (RSV), gastroesophageal reflux disease, and seizures; however, no definite scientific evidence links ALTE as events that will lead to SIDS.
  • SIDS is not caused by immunizations or bad parenting.
  • SIDS is not contagious or hereditary.
  • SIDS is not anyone's fault.

What are the risk factors for SIDS?

Research studies continue to demonstrate a greater risk for SIDS among male infants. SIDS is observed more frequently during winter months than summer months, although this distribution is not as pronounced in recent years as it had been in the past. In the United States, both African-American and Native-American infants have a higher rate of SIDS than do Caucasian, Hispanic, and Asian infants.

Certain infant-care practices have an effect on the risk for SIDS. Most notable is the increased risk associated with the placement of infants on their stomachs (prone sleep position) for sleep. The "Back to Sleep" campaign was launched in the United States in 1994 and embodies a public-health effort encouraging families to place infants on their backs (supine sleep position) to sleep. Since the start of this campaign, SIDS rates have dropped 50% in the United States. Similar drops have been observed worldwide, highlighting the importance of the supine sleep position for infants.

Other factors increasing the risk for SIDS include exposure to cigarette smoke, bed-sharing or co-sleeping, over-bundling or the covering of the infant's head by bed covers, loose bedding, or blankets. Research studies continue to suggest that breastfeeding and pacifier use may reduce the risk of SIDS.

How is SIDS diagnosed?

Sudden infant death remains an unpredictable, unpreventable, and largely inexplicable tragedy. The baby is seemingly healthy without any sign of distress or significant illness prior to the incident.

  • Death occurs rapidly while the infant is sleeping.
  • Typically, it is a silent event. The baby does not cry.
  • The infant usually appears to be well developed, well nourished, and is generally felt to be in good health prior to death. Minor upper respiratory or gastrointestinal symptoms due to viruses like respiratory syncytial virus (RSV) are not uncommon in the last two weeks preceding SIDS.

Sudden, unexpected infant death (SUID) is a general term used for the circumstance of an infant death which occurs suddenly and in an unexpected manner. SIDS is a diagnosis of exclusion, meaning that other causes of death must be ruled out. The cause of an infant's death can be determined only through a process of collecting information and conducting, at times, complex forensic tests and procedures. All other recognizable causes of death are investigated prior to making the diagnosis of SIDS.

Four major avenues of investigation aid in the determination of a SIDS death: postmortem lab tests, autopsy, death-scene investigation, and the review of victim and family case history.

  • Postmortem laboratory tests are done to rule out other causes of death (for example, electrolytes are checked to rule out dehydration and electrolyte imbalance; bacterial and viral cultures are obtained to evaluate whether an infection was present). In SIDS, these laboratory tests are generally not revealing.
  • An autopsy provides clues as to the cause of death. In 15%-25% of sudden, unexpected infant deaths specific abnormalities of the brain or central nervous system, the heart or lungs, or infection may be identified as the cause of death. The autopsy findings in SIDS victims are typically subtle and yield only supportive, rather than conclusive, findings to explain SIDS.
  • A thorough investigation of the death scene consists of interviewing the parents, other caregivers, and family members, collecting items from the death scene, and evaluating that information. A detailed scene investigation may reveal a recognizable and possibly preventable cause of death. Death scene investigations have helped to identify factors in the infant sleep environment that are potentially unsafe. These include soft, padded, or plushy objects that may obstruct an infant's airway, posing a suffocation hazard.
    • A parent or caregiver may be asked these questions:
      • Where was the baby discovered?
      • What position was the baby in?
      • Were there any objects within the sleep location that could have interfered with normal infant breathing?
      • When was the baby last checked? Last fed?
      • How was the baby sleeping?
      • Where there any recent signs of illness?
      • Was the infant taking any medication, either prescription or over the counter?
  • You should let your doctor know about any family or infant medical history. Family history to note would include any previous history of unexplained infant death, sudden cardiac death, and metabolic or genetic disorders, for example.

Quick GuideBaby's First Year: Month to Month Development Milestones

Baby's First Year: Month to Month Development Milestones

Can SIDS be prevented?

There is currently no way to predict which infants are at risk for SIDS. SIDS has been linked to certain infant-specific and sleep-environment factors. Therefore, observing the following precautions has reduced the risk of SIDS for many infants.

  • Sleep position and the local sleep environment: Educate babysitters, day-care providers, grandparents, and everyone who cares for your baby about SIDS risk and the importance of observing the latest advice related to safe infant sleep offered in the original "Back to Sleep" campaign and updated in the recent "Safe to Sleep" initiative. Safe to Sleep ( messages highlight the importance of the back sleep position with emphasis on safety surrounding the infant sleep environment and safe sleep conditions:
    • Back to sleep: You should place your baby on his or her back to sleep at night and nap time.
      • You should avoid fluffy, loose bedding in your baby's sleep area.
      • Keep your baby's face clear of coverings.
      • Be careful not to overheat your baby by overdressing or adding unnecessary covers.
      • You may offer your baby a pacifier when placed for sleep. If it falls out there is no need to replace it.
      • Don't allow anyone to smoke around your baby.
      • Use a firm mattress in a safety-approved crib with a tight fitting sheet. Commercial products, including "breathable mattresses" and infant positioning devices marketed to "reduce SIDS risk" should be avoided. Many of these products have intuitive designs, but have not been scientifically validated to reduce SIDS risk. The use of infant positioners has been linked to deaths due to suffocation in a recently released report from the Consumer Product Safety Commission.
      • Do not use a car seat, carrier, swing, or similar product as your baby's everyday sleep area. Never place your baby to sleep on soft surfaces, such as on a couch or sofa, pillows, quilts, sheepskins, or blankets.
      • Do not allow your baby to sleep alongside another person. The risk of unintentional smothering is too great.
      • Your baby's crib may be placed in your room. Room sharing (but not bed-sharing) has been shown to be protective against SIDS and other sleep-related causes of infant death. If you bring your baby into bed with you to breastfeed, make sure you return your baby to their crib or bassinet when they have completed their feeding.
      • Keep all "well-child" appointments, including immunizations.
  • Home monitoring: The use of home cardiorespiratory monitors for infants perceived to be at risk of SIDS is still controversial. Doctor-prescribed monitors are available that sound an alarm if the baby's breathing or heartbeat stops. These monitors use three electrodes to detect movements of the chest wall and monitor respiratory rate and heart rate. In case of breathing irregularities or decreased heart activity, the device gives off an audible and/or visual alarm. The choice of electronic monitor may measure heart rate, respiratory rate, and pulse oximetry (blood oxygen saturation). The information recorded can be downloaded and periodically and examined by a doctor.
    • Current studies still echo the National Institutes of Health (NIH) Consensus Report on SIDS. To date, no reports scientifically demonstrate the effectiveness of home monitoring for siblings of SIDS victims (babies born after a family has had a child die of SIDS).
    • Currently, certain guidelines exist for use of home cardiorespiratory monitoring:
      • Infants with one or more life-threatening episodes in which the baby turned blue or became limp requiring mouth-to-mouth resuscitation or vigorous stimulation and during hospitalization are identified as having abnormal control of heart or lung function.
      • Symptomatic preterm infants with apnea of prematurity
      • Infants with certain diseases or conditions that include central (brain related) breathing irregularities
      • If families have questions related to the use of home monitors, they should seek assistance from their child's primary medical care provider.

Does the supine (back) sleep position cause any problems for infants?

Recent studies have evaluated the effect of back sleeping on an infant's motor development. Babies younger than 1 year of age who slept on their backs showed slightly decreased upper trunk strength as reflected in mild delays in their ability to crawl, sit upright unassisted, or pull to stand.

  • However, it is important to emphasize that face-up sleepers still attained these milestones within the accepted time range for normal development. No significant difference in gross motor development was seen by the time either infant group started to walk.
  • Parents should incorporate a certain amount of tummy time while the infant is awake and observed. This type of play while baby is on his or her tummy is recommended for developmental reasons and may also help to prevent flattening of parts of the skull, called plagiocephaly, from developing or persisting on the back of the head.

What support is available to parents who are coping with an infant loss due to SIDS?

Most areas within the United States have access to support services for families following a SIDS death. Each family's grief is unique. However, many families that have experienced SIDS have found it helpful to use the counseling resources that may be provided through public-health nursing agencies, local coroner, or medical examiner offices, or information and counseling programs based at many children's hospitals across the country.

Losing a child is a unique crisis for any family, especially when the child has died suddenly, unexpectedly, and for no apparent reason.

  • Do not blame yourselves! Losing a child to SIDS is not your fault.
  • There are typically no warning signs or symptoms that you could have recognized or prevented.

Grieving is a normal process when dealing with the loss of a loved one. Family, friends, neighbors, workplace, or faith communities may all serve as sources of support. It is important to remember that you are not alone. There are formal support groups and counseling programs available to help you cope with your loss. For further information, you may contact these groups:

National Institute of Child Health & Human Development, NICHD/Back to Sleep Campaign
31 Center Drive, Room 2A32
Bethesda, MD 20892-2425
Phone: 800-370-2943
Fax: 301-496-7101

First Candle (SIDS Alliance)
2105 Laurel Bush Road, Suite 201
Bel Air, MD 21015
800-221-7437 (toll free)

Association of SIDS and Infant Mortality Programs (a national network of SIDS support groups)

Minnesota Sudden Infant Death Center
2525 Chicago Avenue South
Minneapolis, MN 55404

National SUID/SIDS Resource Center
The Resource Center is funded by the U.S. Department of Health and Human Services, Health Resources and Services Administration, Maternal and Child Health Bureau.
2115 Wisconsin Avenue, NW, Suite 601
Washington, DC 20007
866-866-7437 (toll free)

Where can people get more information about sudden infant death syndrome (SIDS)?

"Sudden Infant Death Syndrome (SIDS) and Sudden Unexpected Infant Death (SUID)," U.S. Centers for Disease Control and Prevention

American Academy of Pediatrics

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Medically reviewed by Douglas Barton, MD; Board Certified Pediatrics


Carolan, Patrick. "Sudden Infant Death Syndrome." Oct. 1, 2009. <>.