Sudden infant death syndrome (SIDS) is a sudden and unexpected death of a seemingly healthy infant, usually less than one year of age. In order to be considered a case of SIDS, the death must be unexplained, even after a full investigation. SIDS usually occurs while the baby is asleep with no outward signs of distress or struggle - the infant may simply stop breathing.
Most deaths occur among infants under 6 months of age, with the majority occurring under 4 months of age. The syndrome is more common in male babies than in female babies.