Why Is My Newborn Not Sleeping at Night?

Newborns do not sleep at night because they are born without a functioning internal clock. The brain structure responsible for producing melatonin, the hormone that signals nighttime drowsiness, is physically present at birth but cannot actually synthesize the hormone until a baby is roughly four to six months old. Until that system comes online, your newborn has no biological way to distinguish night from day. Combine that with a stomach the size of a cherry that empties in about an hour, and you have a baby who wakes around the clock out of pure physiological necessity rather than stubbornness.

The Missing Clock

Adults take for granted the internal rhythm that makes them sleepy at night and alert during the day. That rhythm is driven largely by melatonin, produced by a small gland deep in the brain called the pineal gland. In newborns, this gland exists but is essentially offline. The cells that produce melatonin need to mature after birth, and the nerve fibers that connect those cells to the brain’s light-sensing system only grow in during the first months of life. Even the genetic programs that guide this maturation unfold on their own postnatal timeline. The result is a genuine melatonin deficiency that lasts until somewhere around four to six months of age.¹ For premature babies, or those delivered by cesarean section, the wait can be even longer.

Without melatonin, your baby’s sleep is governed almost entirely by hunger and comfort. They cycle between sleeping and waking in short bursts of roughly one to three hours, with no preference for doing so at any particular time of day. This is not a problem to solve; it is a stage to get through. The circadian system will switch on, but it develops at its own pace and cannot be rushed.

Why the Feedings Cannot Wait

Even if a newborn’s internal clock were working perfectly, hunger would still wake them every couple of hours. Research on neonatal stomach physiology found that a newborn’s stomach holds about 20 milliliters, which translates to a feeding interval of roughly one hour. That volume lines up with how quickly breast milk passes through the stomach and with the length of a normal newborn sleep cycle.² In practice, most newborns manage slightly longer stretches, especially overnight, but the basic constraint is real: a tiny stomach empties fast, and an empty stomach wakes a baby up.

Formula-fed babies sometimes sleep slightly longer stretches because formula takes longer to digest than breast milk. But the difference is modest and does not change the overall pattern of frequent nighttime waking. Whether breast or bottle, your newborn genuinely needs those calories around the clock. Rapid brain growth and metabolic demands in the first weeks of life do not pause for the night.

How Breast Milk Helps Set the Clock

One fascinating wrinkle is that breast milk itself contains melatonin, and the concentration follows the mother’s circadian rhythm. Milk expressed at night has significantly more melatonin than milk expressed during the day. Studies have found that nighttime breast milk peaks in melatonin content in the hours after midnight, while daytime milk has levels so low they are often undetectable.³ Breast milk is considered the main natural source of melatonin for young infants, and researchers believe these time-of-day shifts in milk composition may help nudge a baby’s developing circadian system in the right direction.⁴

Breast milk also contains cortisol, a stress-related hormone that peaks in the morning. So the milk your baby gets at a 6 a.m. feeding has a different hormonal signature than what they get at 2 a.m. This has led some researchers to caution against mixing up stored milk from different times of day, since feeding a baby “morning milk” at bedtime could theoretically send conflicting signals. The science here is still emerging, but it is an interesting example of how a mother’s body tries to compensate for her baby’s missing clock.

Light Exposure Matters More Than You Think

Since a newborn cannot produce their own melatonin, environmental cues become important stand-ins. The strongest one is light. A scoping review of research on infant circadian development found consistent evidence that cycling between bright conditions during the day and dim conditions at night helps babies establish a day-night rhythm sooner.⁵ One study of preterm infants found that babies in a nursery where light and noise were reduced between 7 p.m. and 7 a.m. slept longer, fed less, and gained more weight compared to babies in a nursery with constant lighting.⁶

For parents at home, a separate study of six- to twelve-week-old babies found that infants who slept better at night had been exposed to more light during the early afternoon hours.⁷ The practical takeaway is straightforward: keep your home reasonably bright during the day, especially in the afternoon. At night, use dim lighting for feeds and diaper changes. You are not training the baby to sleep through the night overnight, but you are feeding information to a circadian system that is slowly wiring itself up.

Their Sleep Is Built Differently

Even when newborns are asleep, the quality of that sleep looks nothing like adult sleep. A large proportion of newborn sleep is active sleep, which is the infant equivalent of REM sleep. During active sleep, babies twitch, grimace, breathe irregularly, and sometimes cry out briefly. Parents often interpret these movements as signs that the baby is waking up, but the baby may still be fully asleep. Over the first months, the proportion of active sleep gradually decreases while quiet sleep (the deeper, stiller kind) increases.⁸

This matters practically because intervening every time a newborn squirms or whimpers can actually interrupt a sleep cycle that would have continued on its own. Pausing for a moment before responding, when safe, can sometimes let the baby settle back into sleep. Longitudinal research tracking babies from birth to one year identified longer parental response times to nighttime awakenings at three months as one of the predictors of a baby developing self-soothing skills by twelve months.⁹ That does not mean ignoring a hungry or distressed newborn. It means learning to distinguish between a brief noise during active sleep and a genuine wake-up.

Reflux and Discomfort

Some newborns who seem especially restless at night may be dealing with gastroesophageal reflux, where stomach contents flow back up the esophagus. Reflux is common in young infants because the muscular valve at the top of the stomach is still maturing. A study monitoring infant sleep stages during reflux episodes found that the onset of a reflux episode was significantly associated with a change in sleep stage, meaning the reflux itself was disrupting sleep rather than the baby happening to wake for other reasons.¹⁰

Signs that reflux might be behind your baby’s nighttime fussiness include arching the back during or after feeds, spitting up frequently, and seeming especially uncomfortable when placed flat on their back. Most infant reflux resolves on its own as the digestive system matures, but if feeds are consistently painful or your baby is not gaining weight, your pediatrician can help determine whether treatment is needed.

Why Frequent Waking May Be Protective

It is worth understanding that not all of a newborn’s frequent waking is a flaw in the system. From a safety standpoint, the ability to wake easily may reduce the risk of sudden infant death syndrome (SIDS). Sleep laboratory studies have shown that certain risk factors for SIDS, including overheating and exposure to cigarette smoke, reduce a baby’s arousability, while protective factors like breastfeeding enhance it.¹¹ A baby who cannot rouse easily in response to a breathing difficulty or a drop in oxygen is at greater risk. So while frequent waking is exhausting for parents, it reflects a nervous system that is responding appropriately to its environment.¹²

This is one reason safe sleep recommendations emphasize keeping the room at a comfortable temperature and placing babies on their back to sleep. Overheating does not just make a baby uncomfortable; it may actually dampen the arousal reflexes that serve as a safety net. Research on sleep and thermoregulation in newborns found that sleeping in a cool environment increases the proportion of active sleep, and while that means lighter, more interruptible sleep, it also means the baby’s thermoregulatory processes stay engaged.¹³

Room Temperature and Overdressing

Parents often worry their newborn is cold at night and pile on layers. A study measuring what parents actually do at home found that when 3-to-4-month-old babies were put down in rooms averaging about 18°C (around 65°F), parents compensated for dropping nighttime temperatures by nearly tripling the insulation from clothing and wrapping. Despite what looked like dramatic overbundling, most babies maintained normal body temperatures.¹⁴ The takeaway is not that overbundling is fine; the concern is that excessive insulation in a warm room can lead to overheating, which is both a sleep disruptor and a SIDS risk factor. A room temperature between roughly 16°C and 20°C (61–68°F) with appropriate sleepwear is generally what pediatric guidance suggests.

White Noise and Other Soothing Strategies

White noise has become a popular tool for helping newborns sleep, and the evidence does support it. Across multiple randomized controlled trials, white noise has been shown to shorten the time it takes babies to fall asleep, improve sleep onset, and reduce the number of awakenings.¹⁵ One study of premature infants found that white noise increased sleep duration by about two hours compared to the pre-treatment period and reduced the number of awakenings.¹⁶

Why it works is partly about masking household sounds that might startle a light sleeper, and partly about recreating the kind of constant, low-frequency sound environment a baby experienced in the womb. The practical advice is to keep the volume moderate and the source at a reasonable distance from the baby’s head. White noise is a tool, not a cure; it can smooth the edges of nighttime waking but will not override hunger or an immature circadian system.

Prenatal Stress and Newborn Sleep

One underappreciated factor is that a baby’s sleep patterns may be influenced by what happened before birth. A longitudinal study found that higher levels of maternal stress and worry during pregnancy were associated with increased sleep problems in children after birth, and the effect was particularly pronounced in boys. Maternal prenatal stress explained about 23% of the variance in sleep problems for male infants, compared to only 1% for females.¹⁷ The proposed mechanism involves stress hormones crossing the placenta and affecting the development of the fetal stress-response system, which in turn may predispose the baby to more disrupted sleep.

This is not something to feel guilty about. Pregnancy is stressful, and knowing about this link does not give parents a time machine. But it does suggest that if your baby seems especially wakeful compared to peers, there may be prenatal factors at play that have nothing to do with what you are doing now.

Growth Spurts and Sleep Disruptions

Parents often notice that just when their baby seemed to be settling into slightly longer stretches, everything falls apart for a few days. Growth may be part of the explanation. Research tracking individual infants found that bursts of physical growth in length were associated with increases in both total daily sleep and the number of sleep bouts, with a time lag of zero to four days. Each additional hour of sleep was associated with higher odds of a growth spurt occurring within that window.¹⁸ So the baby who suddenly wants to nap more and eat more for a few days may be literally growing.

These periods are temporary, and while they can feel like a regression, they are actually a sign that development is proceeding normally. Trying to maintain a rigid schedule through a growth spurt typically frustrates both baby and parent. Riding it out and returning to normal routines afterward tends to work better.

The Toll on Parents

Knowing the biology does not make 3 a.m. feedings easier. A study of mothers of six-month-olds found that the rate of clinically significant depression scores was about double among mothers of chronically waking infants compared to mothers whose babies did not wake during the night.¹⁹ The relationship between infant sleep and parental mental health runs in both directions: a depressed parent may perceive nighttime waking as more distressing, and chronic sleep deprivation genuinely worsens mood and coping. If you find that nighttime parenting is affecting your ability to function or enjoy your baby during the day, that is worth mentioning to your healthcare provider. The baby’s waking pattern is developmentally normal, but your own mental health still matters.

When Longer Stretches Start

Most babies begin consolidating nighttime sleep somewhere between three and six months, which lines up with the maturation of melatonin production and the gradual shift toward more quiet sleep. But the variability between individual babies is enormous. Some start sleeping five- or six-hour stretches by two months; others are still waking multiple times a night well past six months. Both ends of that range can be normal.²⁰

What you can do in the meantime is stack the environmental factors in your favor: bright light during the day, dim light at night, consistent bedtime routines, a comfortably cool room, and feeding your baby when they are hungry without worrying that you are creating bad habits. You are not. A newborn who eats at night is responding to a real physiological need. The habits conversation becomes relevant later, once the circadian and digestive systems have matured enough to support longer sleep windows. For now, the most useful thing to know is that this phase ends, and your baby’s biology is already working to get there.