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Research on Other SIDS Risk Factors

In addition to placing babies on their backs to sleep for naps and at night, as discussed earlier, parents and caregivers can reduce the risk of SIDS and other sleep-related causes of infant death by guarding against several other sleep environment dangers.

Some of these include:

Soft Sleeping Surfaces and Loose Bedding

Studies have found that sleeping on soft surfaces, such as couches and soft mattresses, is a significant risk factor for SIDS.1 For example, in 2003, an NICHD-supported study showed that placing an infant to sleep on soft bedding posed five times the risk of SIDS as sleeping on firm bedding, such as on a safety-approved crib mattress. More striking, though, was the fact that infants who slept on their stomachs on soft bedding were at 21 times greater risk for SIDS than were infants who slept on their backs on firm bedding.2

In addition, soft and loose bedding can increase the potential risk of suffocation.3 The Consumer Product Safety Commission has reported that the majority of sleep-related infant deaths in its database are related to suffocation involving pillows, quilts, and extra bedding.4

Researchers do not know why sleeping on such surfaces increases the risk of SIDS, but they warn that the research findings suggest the practice is highly dangerous.5 The U.S. Consumer Product Safety Commission and the AAP jointly recommend that babies sleep on their backs on a safety-approved* mattress, free of loose bedding, including pillow-like stuffed toys and bumper pads.6

* Visit the U.S. Consumer Product Safety Commission website for more information about crib safety:

Overheating During Sleep

Babies should be kept warm during sleep, but not too warm. Studies show that an overheated baby is more likely to go into a deep sleep from which it is difficult to arouse.7,8,9,10,11   Some evidence indicates that increased SIDS risk is associated with excessive clothing or blankets and a higher temperature in the room.

SIDS risk is higher for infants who sleep on a soft surface or with their heads covered than for infants who sleep on a firm surface or without their heads covered. It is not known whether the risk associated with head covering is related to overheating, lack of oxygen, or re-breathing exhaled air. We do know that it is a particular concern, it can be quite dangerous for some infants, and it may contribute to SIDS.12

Increased SIDS risk also has been associated with the season of the year. In the past, SIDS deaths have been more common during cold weather—possibly because infants are more likely to be overdressed or placed under heavier blankets, which may cause them to overheat—but statistics indicate that this association seems to be waning.13 Studies also have found that overheating may increase the risk of SIDS for a baby who has a cold or infection.

Parents and caregivers should not overdress babies and should keep the thermostat at a comfortable temperature. In general, if the room temperature is comfortable for an adult, then it is appropriate for a baby.14

Smoking During Pregnancy and Smoke in the Infant's Environment

Infants whose mothers smoke during or after pregnancy are at greater risk of SIDS.15 Infants born to mothers who smoked during pregnancy are three times more likely to die of SIDS than those born to mothers who did not smoke during pregnancy. Exposure to passive smoke (sometimes called secondhand smoke) in the household also doubles a baby's risk of SIDS.16,17

Exactly how smoking during pregnancy affects the infant is not clear, but smoking might negatively affect development of the nervous system. Studies of the mechanisms underlying the association between smoking and SIDS have found that, during the last half of pregnancy, changes occur in nicotine-binding sites on the baby's brain stem, specifically in areas involved with arousal, heart and breathing functions, sleep, and body movement control.18

Infants who died from SIDS have a higher nicotine concentration in their lung tissue compared with infants who did not die from SIDS.19 This finding supports the statement that tobacco smoke exposure in the postnatal environment is important in SIDS risk.20,21 However, the mechanism for the association between secondhand smoke and SIDS is unknown.

Bed Sharing

Bed sharing among infants and family members, particularly among adults and infants, is common in some cultures in the United States.22 Many mothers share a bed with their infant because it makes breastfeeding easier and enhances bonding. Even though some believe that bed sharing might reduce the risk of SIDS because the parent is nearby to monitor the baby, studies do not support bed sharing as protective strategy for SIDS.23

On the contrary, evidence is growing that bed sharing increases the risk for SIDS and can also lead to suffocation, entrapment or injury.24 In some situations, bed sharing can compound the risk posed by other factors. For example, the risk for SIDS is even higher than either risk factor alone when bed sharing occurs with:

  • A mother who smokes, has recently consumed alcohol, or is fatigued
  • The infant is covered by a blanket or quilt
  • There are multiple bed-sharers25,26,27,28

Research has shown that the presence of other children in the bed increases the risk of SIDS more than fivefold.29 In addition, bed sharing in an adult bed not designed for an infant exposes the infant to additional risks for accidental injury and death, such as suffocation, asphyxia, entrapment, falls, and strangulation. Infants younger than 4 months of age and those born prematurely or with low birth weight are at highest risk. This may be because their lack of motor skills and muscle strength make it difficult to readjust and avoid potential threats.30

Bed sharing with infants—even when mothers do not smoke—is also a risk factor for SIDS.31,32,33

A baby sleeps on her back in a bassinet, which is next to her mother's bed. The mother lies in her own bed and rests her hand on the side of the baby's bassinet.The safest alternative to bed sharing may be room sharing, a situation in which the infant shares a room with the parents, but has his or her own crib, bassinet, or sleep space.34,35 The AAP recommends keeping the baby's sleep area close to, but separate from, where others sleep. Parents who wish to room share can place the infant's crib near the mother for easy breastfeeding and should return the infant to his or her own sleep area after breastfeeding. Families also should follow all other recommendations to reduce the risk SIDS and sleep-related causes of infant death.

Unaccustomed Sleep Position

NICHD-supported research found that infants who are accustomed to sleeping on their backs but who are then placed to sleep on their stomachs or sides are at an increased risk of SIDS—greater than the increased SIDS risk experienced by infants who are always placed on their stomachs or sides.36

A 1999 study found that if infants who were usually placed to sleep on their back were then placed to sleep on their stomach or side, their risk of SIDS was seven to eight times greater than that of infants always placed to sleep on their stomach or side.37

Make sure that babies always sleep on their backs. Every sleep time counts.

Parents, caregivers, grandparents, babysitters, siblings—everyone in charge of putting baby to sleep should place the baby on his or her back to sleep for every sleep time.

  1. American Academy of Pediatrics, Task Force on Infant Sleep Position and Sudden Infant Death Syndrome. (2000).
  2. Hauck, F. R., et al. (2003). Sleep environment and the risk of sudden infant death syndrome in an urban population: The Chicago Infant Mortality Study. Pediatrics, 111(Suppl. 5), 1207-1214.
  3. Kemp, J. S., et al. (2000). Unsafe sleep practices and an analysis of bed-sharing among infants dying suddenly and unexpectedly: result of a four-year, population-based, death-scene investigation study of sudden infant death syndrome and related deaths. 2000. Pediatrics, 106(3), 1-8..
  4. Chowdhury, R. T. (2010). Nursery Product-Related Injuries and Deaths Among Children Under Age Five. Washington, DC: U.S. Consumer Product Safety Commission.
  5. American Academy of Pediatrics, Task Force on Sudden Infant Death Syndrome. (2005).
  6. U.S. Consumer Product Safety Commission. (2012). Crib safety tips: Use your crib safely [Electronic version]. Retrieved June 19, 2013, from
  7. Fleming, P. J., Gilbert, R., & Azaz, Y. (1990). Interaction between bedding and sleeping position in the sudden infant death syndrome: A population-based case-control study. British Medical Journal, 301, 85-89.
  8. Gilbert, R., Rudd, P., & Berry, P. J. (1992). Combined effect of infection and heavy wrapping on the risk of sudden unexpected infant death. Archives of Disease in Childhood, 67, 171-177.
  9. Ponsonby, A. L., Dwyer, T., Gibbons, L., Cochrane, J. A., Jones, M. E., & McCall, M. J. (1992). Thermal environment and SIDS: Case-control study. British Medical Journal, 304, 277-282.
  10. Ponsonby, A.L., Dwyer, T., Gibbons, L. E., Cochrane, J. A., & Wang, Y. G. (1993). Factors potentiating the risk of sudden infant death syndrome associated with prone position. New England Journal of Medicine, 329, 377-382.
  11. Williams, S. M., Taylor, B. J., & Mitchell, E. A. (1996). Sudden infant death syndrome: Insulation from bedding and clothing and its effect modifiers. International Journal of Epidemiology, 25, 277-282.
  12. Blair, P. S., Mitchell, E. A., Heckstall-Smith, E. M., & Fleming, P. J. (2008). Head covering: A major modifiable risk factor for sudden infant death syndrome—a systemic review.. Archives of Disease in Childhood. 93(9), 778-783.
  13. Malloy, M. H., & Freeman, D. H. (2004). Age at death, season, and day of death as indicators of the effect of the Back to Sleep program on sudden infant death syndrome in the United States, 1992–1999. Archives of Pediatric and Adolescent Medicine, 158, 359-365.
  14. American Academy of Pediatrics, Task Force on Infant Sleep Position and Sudden Infant Death Syndrome. (2000).
  15. American Academy of Pediatrics, Task Force on Infant Sleep Position and Sudden Infant Death Syndrome. (2000).
  16. Ariagno, R. (1994). Smoking and the risk for SIDS [Electronic version]. Retrieved July 5, 2005, from
  17. Schoendorf, K. C., & Kiely, J. L. (1992). Relationship of sudden infant death syndrome to maternal smoking during and after pregnancy. Pediatrics, 90(6), 905-908.
  18. Ariagno, R. (1994).
  19. McMartin, K. I., Platt, M. S., & Hackman, R. (2002). Lung tissue concentrations of nicotine in sudden infant death syndrome (SIDS). Journal of Pediatrics, 140, 205-209.
  20. McMartin, K. I., et al. (2002).
  21. Anderson, H. R., & Cook, D. G. (1999). Passive smoking and sudden infant death syndrome: Review of the epidemiological evidence. Thorax, 54, 365-366.
  22. Willinger, A., Ko, C., Hoffman, H., Kessler, R., & Corwin, M. (2003). Trends in infant bed sharing in the United States, 1993–2000: The National Infant Sleep Position Study. Archives of Pediatric and Adolescent Medicine, 157, 43-49.
  23. Willinger, A., et al. (2003).
  24. American Academy of Pediatrics, Task Force on Infant Sleep Position and Sudden Infant Death Syndrome. (2011). Technical Report -SIDS and other sleep-related infant deaths: expansion of recommendation for a safe infant sleeping environment. Pediatrics, 128(5), 1030-1039.
  25. Hauck, F. R., et al. (2003). Sleep environment and the risk of sudden infant death syndrome in an urban population: The Chicago Infant Mortality Study. Pediatrics, 111(Suppl. 5), 1207-1214.
  26. Scheers, N. J., Rutherford, G. W., & Kemp, J. S. (2003). Where should infants sleep? A comparison of risk for suffocation of infants sleeping in cribs, adult beds, and other sleeping locations. Pediatrics, 112(4), 883-889.
  27. Carpenter, R. G., et al. (2004). Sudden unexplained infant death in 20 regions in Europe: Case-control study. Lancet, 363, 185-191.
  28. Matthews, T., McDonnell, M., McGarvey, C., Loftus, G., & O'Regan, M. (2004). A multivariate "time based" analysis of SIDS risk factors. Archives of Disease in Childhood, 89, 267-271.
  29. Hauck, F. R., et al. (2003).
  30. Vennemann, M., et al. 2011. Bed sharing and the risk of sudden infant death syndrome: Can we resolve the debate? Journal of Pediatrics, 160(1), 44-48.
  31. Carpenter, R. G., et al. (2004).
  32. Tappin, D. M., Ecob, R., & Brooke, H. (2005). Bedsharing, roomsharing, and sudden infant death syndrome in Scotland: A case-control study. Journal of Pediatrics, 147(1), 32-37.
  33. Blair, P. S., et al. (1999). Babies sleeping with parents: Case-control study of factors influencing the risk of sudden infant death syndrome. British Medical Journal, 319(7223), 1457-1462.
  34. Carpenter, R. G., et al. (2004).
  35. Tappin, D. M., et al. (2005).
  36. Li, D. K., et al. (2003). Infant sleeping position and the risk of sudden infant death syndrome in California, 1997–2000. American Journal of Epidemiology, 157(5), 446-455.
  37. Mitchell, E. A., Thach, B. T., Thompson, J. M. D., & Williams, S. (1999). Changing infants' sleep position increases risk of sudden infant death syndrome. Archives of Pediatric and Adolescent Medicine, 153(11), 1136-1141.
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