Sudden infant death syndrome (SIDS) is the unexpected, sudden death of a child under age 1 in which an autopsy does not show an explainable cause of death.

SIDS rates have dropped dramatically since 1992, when parents were first told to put babies to sleep on their backs or sides to reduce the likelihood of SIDS. Unfortunately, SIDS remains a significant cause of death in infants under one year old. Thousands of babies die of SIDS in the United States each year.

The cause of SIDS is unknown, although there are several theories. Many doctors and researchers now believe that SIDS is not a single condition that is always caused by the same medical problems, but infant death caused by several different factors.

These factors may include problems with sleep arousal or an inability to sense a build-up of carbon dioxide in the blood. Almost all SIDS deaths occur without any warning or symptoms when the infant is thought to be sleeping.

SIDS is most likely to occur between 2 and 4 months of age, and 90% occur by 6 months of age. It occurs more often in winter months, with the peak in January. There is also a greater rate of SIDS among Native and African Americans.

The following have been linked to an increased risk of SIDS:

• Babies who sleep on their stomachs
• Babies who are around cigarette smoke while in the womb or after being born
• Babies who sleep in the same bed as their parents
• Babies who have soft bedding in the crib
• Multiple birth babies (being a twin, triplet, etc.)
• Premature babies
• Babies who have a brother or sister who had SIDS
• Mothers who smoke or use illegal drugs
• Teen mothers
• Short time period between pregnancies
• Late or no prenatal care
• Situations of poverty

SIDS affects boys more often than girls. While studies show that babies with the above risk factors are more likely to be affected, the impact or importance of each factor is not well-defined or understood.