Sudden Infant Death Syndrome (SIDS)

What SIDS is, and what it is not

SIDS is a diagnosis made only after a thorough investigation, including an autopsy, a review of the death scene and the baby's medical history, finds no other cause. Deaths from accidental suffocation, strangulation, infection or a hidden medical condition are not SIDS.

SIDS is one type of sudden unexpected infant death (SUID). Others include accidental suffocation and strangulation in bed and deaths from unknown causes. Many safe sleep measures prevent all types.

SIDS is not caused by vaccines, and it is not caused by choking on spit-up in healthy babies who sleep on their backs.

Why it happens: the triple-risk model

Researchers think SIDS occurs when three factors coincide:

1. A vulnerable baby: for example, subtle differences in the brainstem areas that control breathing, heart rate and waking from sleep, or premature birth
2. A critical developmental period: the first 6 months, when control of breathing and arousal is still maturing
3. An outside stressor: stomach sleeping, soft bedding, overheating, or smoke exposure

Most babies can respond to stressors by waking or turning their head. Infections such as bronchiolitis can add stress in the first months. A vulnerable baby may not.

Risk factors

Sleep environment

• sleeping on the stomach or side
• soft surfaces: adult beds, couches, armchairs, pillows, waterbeds
• loose bedding, pillows, bumper pads and soft toys in the crib
• bed-sharing, especially with a parent who smokes, has taken alcohol, drugs or sedating medicines, or is very tired
• sleeping on a couch or armchair with an adult, which is particularly dangerous
• overheating from too many layers or a hot room
• sitting devices such as car seats, swings and slings used for routine sleep

Baby and family factors

• premature birth and low birth weight
• boys are slightly more affected
• smoking during pregnancy or exposure to smoke after birth (see smoking and tobacco addiction)
• alcohol or drug use during pregnancy
• young maternal age and limited prenatal care
• a sibling who died of SIDS

Note that higher rates in some communities reflect differences in risk factors and access to care, not race itself.

How to reduce the risk: safe sleep

The American Academy of Pediatrics recommends:

1. Back to sleep for every sleep, for naps and at night, until age 1. Once a baby can roll both ways, they can stay in the position they choose.
2. A firm, flat, level sleep surface such as a crib, bassinet or play yard that meets current safety standards, with a fitted sheet only. Inclined sleepers are not safe.
3. Nothing else in the sleep space: no pillows, blankets, bumpers, positioners or toys.
4. Room-share without bed-sharing, ideally for at least the first 6 months: keep the baby's crib in the parents' room.
5. Breastfeed if possible; any breastfeeding is protective.
6. Offer a pacifier at naps and bedtime once breastfeeding is established. Do not force it or reinsert it after the baby falls asleep.
7. Avoid smoke, alcohol and drugs during pregnancy and around the baby.
8. Avoid overheating: dress the baby in no more than one extra layer than an adult would wear; no hats indoors for sleep.
9. Keep up with vaccinations.
10. Do not use weighted sleep sacks or weighted swaddles. Stop swaddling once the baby shows signs of trying to roll.
11. Do not rely on home heart and breathing monitors or consumer devices to prevent SIDS.
12. Supervised tummy time while awake helps development and prevents flat spots on the head.

If you fall asleep while feeding in an adult bed, return the baby to their own sleep space as soon as you wake. Avoid feeding on a couch or armchair when you might fall asleep.

Support after a loss

Losing a baby to SIDS is devastating. Grief can overlap with postpartum depression, which deserves treatment in its own right. Parents often feel guilt, even when they did everything right. Support from family, grief counselors, support organizations and other bereaved parents can help. Siblings and grandparents also need support. Talk to your doctor if grief becomes overwhelming, or if you have thoughts of self-harm (call or text 988 in the US).

Parents planning future pregnancies can discuss extra precautions and support with their pediatrician.

Frequently asked questions

What causes SIDS?

The exact cause of SIDS is unknown. It is thought to occur when a vulnerable baby, such as one with subtle differences in brain areas controlling breathing and waking, faces a stress such as stomach sleeping or soft bedding during a critical developmental period in the first months of life.

At what age is SIDS most common?

SIDS is most common between 1 and 4 months of age. About 90% of cases occur before 6 months. The risk falls after 6 months, but safe sleep is recommended until the first birthday.

How can I reduce my baby's risk of SIDS?

Place your baby on their back for every sleep, on a firm, flat surface with no pillows, blankets or toys. Room-share without bed-sharing, breastfeed if possible, offer a pacifier at sleep, avoid smoke exposure and overheating, and keep vaccinations current.

Is it safe for my baby to sleep in a swing or car seat?

Not for routine sleep. Sitting devices can let a baby's head fall forward and block their airway. If your baby falls asleep in one, move them to a firm, flat sleep surface as soon as practical.

Do baby breathing monitors prevent SIDS?

No. Home monitors and wearable devices have not been shown to reduce SIDS and can give false reassurance. Following safe sleep practices is the most effective protection.