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What causes SIDS or sudden infant death syndrome?

No single cause of SIDS has been found. It's believed to result from a combination of a baby's underlying vulnerability, a critical stage of development (usually 2-4 months), and an outside stressor like unsafe sleep conditions.

Known risk factors include tummy or side sleeping, soft bedding, overheating, smoke exposure, prematurity, and bed-sharing, while back sleeping, room-sharing, and breastfeeding lower risk.

Strength of evidence

Good

Based on national guideline statements plus large case-control and cohort studies; because SIDS deaths can't be studied with randomized trials, the evidence is mainly observational rather than experimental.

What the evidence says

The honest answer is that no one knows exactly what causes SIDS. By definition, it's diagnosed only after doctors rule out every other explanation for a baby's sudden death during sleep.

Most experts now think SIDS happens through a 'triple risk' combination: a baby who has some hidden vulnerability (such as differences in brain areas that control breathing or waking up), during a sensitive age window (most deaths happen between 2 and 4 months), plus an outside stress like tummy sleeping, overheating, or secondhand smoke that tips things over the edge.

Known risk factors include sleeping on the stomach or side, soft bedding or soft sleep surfaces, bed-sharing, overheating, prematurity or low birth weight, and smoking or substance use during or after pregnancy. Protective steps include placing babies on their backs for every sleep, room-sharing without bed-sharing for the first six months, breastfeeding, and keeping the home smoke-free.

One reassuring fact: large safety reviews have found no link between childhood vaccines and SIDS, even though the peak vaccination age overlaps with the peak SIDS age.

Sources

✓Reviewed by CH, MD, FRCPC

Reviewed by a specialist physician certified by the Royal College of Physicians and Surgeons of Canada, who has read this answer against the sources listed above and confirmed it reflects them. That is not medical advice about your child. How we review

Answer checked July 29, 2026

Educational information only. Not medical advice, not a diagnosis, and no doctor-patient relationship is created by using this. Founded Parent has not examined your child and does not know their history, so this may not apply to you. In an emergency, call your local emergency number. What Founded Parent cannot do

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