SIDS risk peaks between 1 and 4 months of age. That window accounts for 72% of all SIDS deaths, and more than 90% occur before a baby reaches 6 months. While SIDS can technically happen any time in the first year, the danger drops sharply in the second half of infancy and essentially disappears after age 1.
The Peak Risk Window: 1 to 4 Months
Newborns in their very first weeks are not at the highest risk. SIDS deaths climb steeply around the one-month mark, stay elevated through month four, and then begin to decline. The National Institutes of Health reports that nearly three out of four SIDS deaths fall within that 1-to-4-month range. By six months, the overwhelming majority of risk has passed.
This timing isn’t random. Between one and six months, babies are going through a critical developmental period in which the brain systems that regulate breathing, heart rate, and blood pressure are still maturing. Researchers call this the “triple risk” model: SIDS happens when three things overlap at the same time. First, the baby has an underlying vulnerability, often one that isn’t detectable from the outside. Second, they’re in this critical developmental window. Third, they encounter an external stressor, like sleeping face-down or overheating. Remove any one of those three factors and the risk drops significantly.
Why Some Babies Are More Vulnerable
Studies of infants who died from SIDS have found differences in the brainstem, the part of the brain responsible for automatic functions like breathing and waking up. Specifically, researchers have identified abnormalities in the chemical signaling systems that help a baby sense rising carbon dioxide levels and respond by turning their head, gasping, or waking. In more than 80% of older SIDS cases examined in one study, key areas of the lower brainstem showed altered signaling in the circuits that control these protective reflexes.
In a healthy baby, a brief episode of blocked breathing triggers an automatic response: the baby shifts position, gasps, or cries. In a baby with these brainstem differences, that alarm system may not fire properly. This is why the vulnerability is “latent,” as researchers describe it. The baby appears completely normal until a stressor overwhelms a system that was never fully equipped to handle it.
How Prematurity Shifts the Timeline
Premature babies face a higher overall risk of SIDS, and their peak vulnerability hits earlier in calendar age. Research comparing preterm and full-term infants found that babies born at 24 to 28 weeks of gestation died of SIDS at an average postconceptional age of about 46 weeks, compared to roughly 52 weeks for full-term infants. That’s a gap of 4 to 6 weeks. In practical terms, a baby born two months early may hit their highest-risk period sooner after birth than a full-term baby would, because the critical developmental window is tied more to biological maturity than to birthday.
Winter Months Carry Higher Risk
SIDS has a seasonal pattern. CDC data spanning the 1980s found that infants were about half as likely to die of SIDS in July or August compared to January. The cold season has consistently shown higher rates. The exact reason isn’t fully settled, but two leading explanations involve respiratory infections, which circulate more in winter, and overheating from extra blankets and clothing. Both qualify as external stressors in the triple risk model. Bundling a baby in heavy layers or adding loose blankets to a crib during cold months can raise body temperature and increase the chance that a vulnerable infant won’t rouse from sleep.
Other Factors That Raise Risk
Sleep position is the single most modifiable risk factor. Studies comparing stomach sleeping to other positions have found that prone sleeping increases the likelihood of SIDS by 3.5 to 9.3 times, depending on the study. The “Back to Sleep” campaigns launched in the 1990s cut SIDS rates dramatically, and placing babies on their backs remains the foundation of prevention.
Other established risk factors include male sex, low birth weight, complications during pregnancy or delivery, and multiple births. Exposure to cigarette smoke, both during pregnancy and after birth, is one of the strongest environmental contributors. Soft bedding, couch sleeping, and sharing a sleep surface with another person all increase risk as well.
What Lowers the Risk
Several strategies offer meaningful protection, especially during the high-risk months:
- Back sleeping. Always place your baby on their back for every sleep, including naps.
- Firm, flat surface. Use a crib, bassinet, or portable play yard with a firm mattress and fitted sheet. Nothing else should be in the sleep space: no pillows, blankets, stuffed animals, or bumper pads.
- Room sharing without bed sharing. Having your baby sleep in your room but on a separate surface is protective. Sleeping on a couch or armchair with an infant is particularly dangerous.
- Pacifier use. Offering a pacifier at sleep time has been associated with a 70% reduction in SIDS risk. That protective effect was even stronger when other risk factors were present, such as stomach sleeping or soft bedding, though a pacifier should never be treated as a substitute for a safe sleep environment.
- Avoiding overheating. Dress your baby in no more than one layer beyond what you’d wear comfortably. Skip hats indoors and keep the room at a comfortable temperature.
When the Risk Drops Off
After six months, SIDS becomes uncommon. By the time a baby can roll both ways, lift their head, and shift positions during sleep, many of the mechanical risks diminish because the baby is better equipped to move out of a dangerous position. After age 1, the diagnosis changes entirely. Sudden unexplained deaths in children older than 12 months are classified as SUDC (sudden unexplained death in childhood), a separate and much rarer condition. In the United States, SIDS causes roughly three times as many deaths annually as SUDC, with about 1,529 SIDS deaths recorded in 2022.
The sharpest decline in risk happens between months 4 and 6. If your baby is past the six-month mark, the most dangerous period is behind you, though safe sleep practices should continue through the first year.