General pathology · Paediatric pathology
Sudden infant death syndrome: what is known !
- Topic
It is the unexpected death of a healthy baby during sleep that stays unexplained after a full investigation; sleeping on the back greatly lowers the risk.
Updated 2026-11-01
What it is
Sudden infant death syndrome is the sudden death of an infant under one year that remains unexplained after autopsy, study of the death scene and review of the clinical history. It is a diagnosis of exclusion. It is best explained by the triple-risk model: a vulnerable infant, a critical developmental period and an outside stressor.
Step by step
- A vulnerable infant: brainstem abnormalities in the serotonin circuits that control breathing and arousal.
- A critical period: the first months, while control of breathing, heart rhythm and temperature are still maturing.
- An outside stressor: sleeping prone, face into a soft mattress, rebreathing exhaled air or overheating.
- Faced with hypoxia and hypercapnia, a healthy infant wakes and moves; the vulnerable infant does not wake.
- Asphyxia progresses, causing bradycardia and death during sleep.
What must be ruled out before diagnosing the syndrome
| Cause | Why it is excluded | How it is sought |
|---|---|---|
| Accidental suffocation in bed | Death explained by the sleep environment | Investigation of the scene and position |
| Child maltreatment | A violent death can mimic a sudden death | Autopsy, skeletal survey, retinal examination |
| Long QT syndrome and other channelopathies | Fatal arrhythmia without a visible lesion | Genetic testing of the infant and family |
| Inborn errors of metabolism (MCAD deficiency) | Hypoketotic hypoglycaemia during fasting | Newborn screening and acylcarnitine profile |
| Infections | Unsuspected sepsis, myocarditis or pneumonia | Histology and cultures |
Clinical notes
- Prevention: on the back for every sleep, a firm flat surface, a cot without pillows or toys, room-sharing without bed-sharing.
- Breastfeeding, avoiding tobacco smoke and avoiding overheating are also protective.
- Sudden unexpected infant death groups this syndrome, accidental suffocation in bed and deaths of undetermined cause.
Test yourself
Think of the answer, then tap the question to see it.
At what age is sudden infant death syndrome most common?
Between two and four months of life.
Which three components make up the triple-risk model?
A vulnerable infant, a critical developmental period and an outside stressor, such as sleeping prone.
Why is it considered a diagnosis of exclusion?
Because it is made only when the autopsy, the death scene and the history reveal no other cause.
Which sleeping position lowers the risk?
On the back (supine) for every sleep.
Related
Related conditions
- Sudden infant death syndrome (SIDS)
- Prematurity and its complications
- Long QT syndrome and torsades de pointes
- Child maltreatment (physical abuse, abusive head trauma, neglect)
- Apnoea of prematurity
Elsewhere in DurgiPedia
- Control of breathing, chemoreceptors and lung reflexes
- Medium-chain acyl-CoA dehydrogenase (MCAD)
- Newborn physiology and fetal maturation
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Sudden infant death syndrome: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); About SUID and SIDS | SUID and SIDS | CDC (Centers for Disease Control and Prevention, 2026).
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Representative model, for educational purposes only.