Last reviewed: November 4, 2026 · Updated to match current American Academy of Pediatrics (AAP) safe sleep guidance and CDC data.
Quick answer: Sudden infant death syndrome (SIDS) is the sudden, unexplained death of a baby under 1 year old, usually during sleep, that can’t be explained even after a full investigation. Its exact cause isn’t known, but the risk can be lowered a lot by following safe sleep rules: place your baby on their back for every sleep, on a firm, flat surface with nothing else in the crib, in your room but not in your bed. Breastfeeding, offering a pacifier at sleep time, a smoke-free home and avoiding overheating also lower the risk.
What Is SIDS?
SIDS is one type of sudden unexpected infant death (SUID). The CDC groups SUID into three categories: SIDS, accidental suffocation and strangulation in bed, and deaths from unknown causes. According to the Centers for Disease Control and Prevention (CDC), about 3,400 babies in the US die from SUID each year, and in 2020 about 41% of those deaths were classified as SIDS.
SIDS is most common in babies between 1 and 4 months old, and most cases happen before 6 months, but it can happen any time in the first year. You may hear it called “crib death,” because it usually happens during sleep.
What Causes SIDS?
Researchers don’t know exactly what causes SIDS. The leading explanation is a combination of three things happening at once:
- A vulnerable baby, for example one with differences in the part of the brain that controls breathing and waking up
- A critical age, the first months of life, when these systems are still developing
- An outside stressor, such as sleeping on the stomach, soft bedding near the face, overheating or exposure to smoke
Parents can’t control the first two, but they can remove most of the outside stressors. That’s why safe sleep habits matter so much, and why SIDS rates fell sharply after the “Back to Sleep” campaign began in 1994. It is now called Safe to Sleep.
How to Lower the Risk of SIDS
These are the AAP’s main safe sleep recommendations:
- Back to sleep, every sleep. Place your baby on their back for naps and at night until their first birthday. Once they can roll both ways on their own, you don’t need to turn them back over.
- Firm, flat surface. Use a crib, bassinet or play yard that meets safety standards, with a firm, flat mattress and a fitted sheet. Never use an inclined surface, and don’t let your baby sleep in a car seat, swing or bouncer (move them to their crib if they fall asleep).
- Keep the crib empty. No pillows, blankets, bumpers or stuffed toys. Use a wearable blanket (sleep sack) instead of loose blankets.
- Share a room, not a bed. The AAP recommends your baby sleeps in your room, in their own sleep space, ideally for at least the first 6 months. Never sleep with your baby on a sofa, armchair or couch.
- Breastfeed if you can. Breastfeeding is linked to a lower risk of SIDS.
- Offer a pacifier at sleep time. If you’re breastfeeding, wait until feeding is going well. Don’t force it, and don’t put it back in once your baby is asleep.
- Avoid smoke, alcohol and drugs during pregnancy and after birth. Keep your home and car smoke-free.
- Don’t let your baby get too hot. Dress them in no more than one extra layer than an adult would wear, and keep their head uncovered. See our guide to dressing a baby for sleep in winter.
- Keep up with routine vaccines and checkups.
- Give plenty of supervised tummy time while your baby is awake.
Products to Avoid
- Weighted sleep sacks, weighted swaddles and weighted blankets. The AAP says weighted products on or near a sleeping baby are not safe. Regular, non-weighted sleep sacks are fine and are a safe alternative to blankets.
- Swaddling after your baby starts trying to roll. Swaddling is fine for young babies placed on their back, but stop as soon as your baby shows signs of trying to roll over, often around 2 to 4 months.
- Inclined sleepers, wedges and positioners. These are not safe for sleep. This applies even when your baby is congested: see our guide to the safest sleeping position for a baby with a stuffy nose.
- Products that claim to prevent SIDS. No product, including home breathing or heart-rate monitors, has been shown to lower the risk of SIDS. Following safe sleep habits is what works.
Frequently Asked Questions
When is a baby no longer at risk of SIDS?
The risk is highest between 1 and 4 months and drops after 6 months, but SIDS can happen until 1 year old. Keep following safe sleep rules until your baby’s first birthday.
Is it safe for my baby to sleep on my chest?
Only while you are awake and alert. If you might fall asleep, put your baby down on their back in their own crib or bassinet first.
Are sleep sacks safe?
Yes, regular sleep sacks are a safe replacement for blankets. Weighted sleep sacks and swaddles are not recommended.
The Bottom Line
SIDS is rare, and while its cause isn’t fully understood, safe sleep habits greatly reduce the risk. Put your baby on their back, on a firm, flat surface, with nothing else in the crib, in your room but not your bed. Avoid smoke, overheating and weighted or inclined products, and talk to your pediatrician if you have questions about your baby’s sleep.
This article is for general information and isn’t a substitute for medical advice. Always contact your pediatrician with questions about your baby’s health.
3 Sources
Newborn Stages uses trusted sources, including government health agencies, children’s hospitals and pediatric organizations, to support the facts in our articles. Read our editorial policy to learn how we research, fact-check and keep our content accurate.
- HealthyChildren.org, American Academy of Pediatrics. How to keep your sleeping baby safe: AAP policy explained.
- Centers for Disease Control and Prevention. Data and statistics for SUID and SIDS.
- Safe to Sleep, National Institutes of Health. Safe to Sleep campaign.
Originally written by Jenny Fries, a freelance writer covering technology, business and health. Rewritten and medically updated by the Newborn Stages editorial team in November 2026 to reflect current AAP safe sleep guidance.
