Why Does My Baby Keep Crying at Night? Causes & Fixes

Babies cry at night mostly because their biology demands it. A newborn’s internal clock is not yet functional, their stomach empties remarkably quickly, and their sleep cycles are roughly two-thirds the length of an adult’s. Most of what parents experience as baffling nighttime distress traces back to a handful of well-understood causes, and the majority resolve on their own as the baby’s nervous system matures over the first year.

Their Internal Clock Takes Months to Develop

Adults take for granted that night means sleep and day means wakefulness. Newborns have no such distinction. In the first weeks of life, a baby spends about 70% of the time sleeping, but those sleep episodes are scattered evenly across day and night with no clear rhythm.¹ At two weeks of age, infants sleep in roughly four-hour blocks regardless of whether the sun is up. The brain’s circadian system begins producing a weak day-night pattern around five weeks, but it takes until about 15 weeks before consolidated wake episodes appear during the day and longer stretches of sleep settle into the night. By six to nine months, most babies can manage at least six continuous hours of nighttime sleep.

What this means for you as a parent is straightforward: if your baby is under three to four months old and wakes frequently at night, the problem is not really a problem at all. Their brain literally cannot distinguish night from day yet. Total sleep across the first year stays fairly stable at around 14 hours a day. What changes is the packaging. As the circadian system matures, those 14 hours gradually shift from being sprinkled across the 24-hour cycle to being concentrated at night with daytime naps.¹

Hunger Arrives Faster Than You Expect

Even parents who know babies need frequent feeds are often surprised by just how frequent. A full-term newborn’s stomach holds about 20 milliliters, and at that volume, a feeding interval of approximately one hour aligns with how fast human breast milk empties from the stomach.² That one-hour window also matches the length of a typical newborn sleep cycle, so a baby who wakes crying after a short bout of sleep may simply be hungry again, not in distress for some other reason.

As stomach capacity grows and feeding efficiency improves over the first few months, the intervals between hunger-driven wakeups naturally lengthen. Formula-fed babies sometimes stretch a bit longer between feeds because formula digests more slowly than breast milk, but the basic pattern holds for all newborns: tiny stomachs need frequent refills, and frequent refills mean frequent waking. If your newborn seems hungry again shortly after feeding, that is perfectly consistent with normal physiology.

Short Sleep Cycles Mean More Chances to Wake

Between each cycle of sleep there is a brief moment of near-wakefulness. Adults usually roll over and fall back asleep without remembering it. Babies are worse at that transition. Part of the reason is that their sleep cycles are significantly shorter. A large actigraphy study found that infant sleep cycles averaged about 62 minutes, compared to roughly 81 minutes in their parents, and those infant cycles lengthened by only about 10 minutes over the entire stretch from three to twelve months of age.³

Shorter cycles mean more transitions per night, and each transition is a window where the baby might wake fully and cry. This is a normal feature of infant sleep architecture, not a sign that something is wrong. The good news is that cycles do gradually lengthen, and as they do, the odds of making it through a transition without waking improve. But expecting a young baby to link together several cycles seamlessly is asking their brain to do something it is not yet wired for.

Teething Probably Is Not the Culprit

Teething is one of the most popular explanations parents reach for when nighttime crying flares up in the second half of the first year. It makes intuitive sense: teeth pushing through gums sounds painful, and the timing often coincides with a sleep disruption. But the evidence is surprisingly unsupportive. A study that used overnight video recordings to objectively measure sleep found no significant differences in sleep metrics between nights when a tooth was actively erupting and non-teething nights. More than half of the parents in the study believed teething was disrupting their baby’s sleep, but the objective data did not back them up.⁴

This does not mean teething never causes any discomfort. Drooling, fussiness during the day, and mild gum irritation are real. But when your eight-month-old suddenly starts waking three times a night, teething may be getting the blame for something caused by a developmental milestone or a shift in sleep habits. Jumping to “it’s the teeth” can delay a more useful response.

Motor Milestones Can Temporarily Wreck Sleep

One of the better-supported explanations for sudden sleep regressions in the second half of the first year involves motor development. Learning to crawl is a big deal for a baby’s brain, and it appears to come at a cost. In a study of seven- and eight-month-olds, whether or not an infant had begun crawling predicted 17% of the variation in nightwaking, even after accounting for age and sex. Babies who were already crawling had more bedtime difficulties and more nighttime awakenings than pre-crawlers.⁵

A longitudinal study using actigraphy confirmed the pattern and showed that the disruption was specifically timed to the onset of crawling, not just a general feature of being a certain age.⁶ The same kind of disruption appears again when babies start learning to walk. Infants in the midst of acquiring walking skills had worse sleep than age-matched estimates would predict.⁷

The reassuring part: these disruptions are temporary. Once the new motor skill becomes routine and the brain finishes integrating it, sleep tends to settle back down. If your baby was sleeping reasonably well and then regresses right around the time they start pulling up or cruising, motor development is a much more likely explanation than teething or a sudden behavioral problem.

Colic, Stress, and the Cortisol Connection

Some babies cry more intensely and wake more frequently than their peers, and colic is the label often applied when the crying is excessive and persistent with no obvious medical cause. Research has linked higher morning cortisol levels in colicky infants to more frequent night awakenings and greater crying intensity. The relationship was specifically with how intensely the baby cried, not how long each crying bout lasted, suggesting that the stress-response system is involved in amplifying the distress rather than just prolonging it.⁸

This creates a frustrating cycle for parents. A baby with fragmented sleep produces more stress hormones, which intensifies crying, which makes it harder for the baby and the parents to settle. The cortisol finding helps explain why colicky babies seem so much more agitated than simple hunger or discomfort would justify. It also means that strategies aimed at reducing overall arousal, like keeping the environment calm and predictable during nighttime interactions, may do more good than trying to identify a single trigger.

When Cow’s Milk Allergy Is the Hidden Cause

Most parents do not think of food allergy when their baby wakes and cries repeatedly at night, but research going back decades has documented a real link. In one study, 71 infants were divided into groups: those referred for chronic sleeplessness that had started in the first days of life, those admitted for known cow’s milk intolerance, and a control group with no sleep or allergy complaints. Lab testing revealed immune reactions to milk in all the babies in the first two groups. When cow’s milk was removed from the diet, sleep normalized. When milk was reintroduced as a challenge in the chronic-insomnia group, the sleeplessness returned.⁹

An earlier report on a smaller group of eight infants found the same thing: all had elevated markers for cow’s milk protein allergy, and when switched to a hydrolyzed formula, their night sleep increased to about 10 hours within two weeks, with awakenings becoming only occasional.¹⁰

This does not mean every poorly sleeping baby has a milk allergy. But it is worth considering, especially if other potential signs are present: eczema, frequent spitting up, loose stools, or a family history of allergies. If no other explanation for chronic nighttime waking turns up, bringing the possibility of cow’s milk allergy to your pediatrician’s attention is a reasonable step. A trial elimination of cow’s milk protein, either by switching formula or by the breastfeeding parent removing dairy from their own diet, can produce noticeable improvements within a couple of weeks when allergy is the cause.

Light Exposure and Room Temperature

Two environmental factors that parents can actually control have meaningful effects on how well babies sleep at night. The first is daytime light exposure. Research suggests that greater exposure to bright light during the day, above roughly 100 lux (about the level of a well-lit indoor room or light shade outdoors), helps strengthen the emerging circadian rhythm and promotes better nighttime sleep. Conversely, continuous exposure to steady, dim light around the clock can interfere with circadian development.¹¹ The practical takeaway is simple: get your baby into natural daylight during waking hours and keep things dim in the evening and at night. You are not just creating ambiance; you are helping calibrate their internal clock.

Temperature is the other factor. Anyone who has tried to sleep in a too-warm room knows how disruptive heat can be, and babies are more sensitive to it. One study modeling the relationship found that for every one-degree Celsius increase in nursery temperature, sleep duration dropped by roughly 18 minutes. The effect was statistically significant for temperature but not for humidity, making room warmth the more important variable to manage.¹² Most pediatric guidelines recommend keeping the nursery between about 18 and 21 degrees Celsius (roughly 65 to 70 degrees Fahrenheit). Overdressing the baby or piling on blankets can effectively raise the temperature around them even if the room thermostat reads fine.

Helping Your Baby Learn to Self-Soothe

All babies wake during the night, even those whose parents believe they sleep through. The difference between a baby who “sleeps through” and one who cries is often whether the baby can settle back to sleep on their own after a normal between-cycle arousal. Research has identified several factors that predict self-soothing ability at 12 months: spending less time being held outside the crib over the first year, having longer stretches of quiet sleep as a newborn, and parents waiting a bit longer before responding to awakenings at around three months of age.¹³

That last point is easy to misread as “ignore your crying baby,” which is not what the research is saying. A brief pause before rushing in gives the baby a chance to cycle back to sleep independently. When parents did intervene, the type of soothing mattered. Practices associated with more independent sleep included not routinely feeding the baby to sleep during nighttime wakings, putting the baby into bed drowsy but still awake at around six months, and using lower-stimulus soothing strategies like gentle patting or shushing instead of picking up and rocking.¹⁴

Parents worried about full extinction methods (sometimes called “cry it out”) have alternatives. A pilot study comparing a responsive approach, where the parent stays present and provides comfort while still encouraging independent sleep, against full extinction found that babies in the responsive group actually woke less. Mothers in the responsive group also reported significantly less stress and fewer symptoms of depression, with no differences in cortisol levels between the two groups of infants.¹⁵ The takeaway is that you do not have to choose between your baby crying alone in a dark room and never sleeping well. Graduated, responsive methods exist that support both the baby’s sleep development and the parent’s mental health.

How Culture Shapes What Counts as a Sleep Problem

The definition of “my baby has a sleep problem” depends heavily on where in the world you live. A large cross-cultural survey comparing sleep patterns across predominantly Asian and predominantly Caucasian countries found striking differences. Bedtimes ranged from 7:27 p.m. in New Zealand to 10:17 p.m. in Hong Kong. Total daily sleep ranged from about 11.6 hours in Japan to 13.3 hours in New Zealand. Bed-sharing with parents ranged from under 6% in New Zealand to over 83% in Vietnam.¹⁶

Perhaps most telling, parents in Asian countries were significantly more likely to perceive their child’s sleep as a problem, even though much of the variation in sleep timing reflected cultural norms rather than pathology. In cultures where bed-sharing is standard and later bedtimes are typical, a baby waking several times at night and nursing back to sleep may not generate the same alarm as it would in a culture where solitary sleep in a separate room is the expectation. This does not mean one approach is right and the other wrong. It means that some of the anxiety parents feel about nighttime crying is calibrated to cultural expectations about how babies “should” sleep rather than to anything biologically harmful. If your baby wakes a few times a night but is otherwise healthy, gaining weight, and developing normally, the waking itself may not be the problem. The mismatch between the waking and your expectations might be.

When to Worry and When to Wait

Most nighttime crying in the first year falls into the categories above: an immature circadian clock, hunger, developmental regressions, environmental discomfort, or the baby simply not yet knowing how to link sleep cycles. These are all normal and self-limiting. But certain patterns do warrant a conversation with your pediatrician. Persistent, inconsolable crying that is not explained by hunger or a wet diaper and does not improve with soothing, especially if accompanied by fever, vomiting, unusual stool, or failure to gain weight, can signal an underlying medical issue. As discussed earlier, chronic sleeplessness without other obvious causes deserves a look at possible food allergy.

Ear infections are another common medical cause of sudden-onset night crying that parents sometimes miss, since the pain often worsens when the baby lies flat. If a baby who had been sleeping reasonably well suddenly becomes inconsolable specifically when placed on their back, especially during or shortly after a cold, an ear check is a good idea. Gastroesophageal reflux can also cause discomfort that peaks when the baby is lying down, though mild reflux is extremely common in infants and usually does not need medical intervention unless it affects feeding or weight gain.

For the vast majority of healthy babies, though, nighttime crying is not a symptom to fix but a developmental phase to survive. The circadian system matures, the stomach grows, the motor milestones get absorbed, and the baby gradually learns to resettle. Parental exhaustion during these months is real and cumulative. Research has documented that ongoing sleep disruption from infant crying can trigger depressive symptoms and reduce parents’ ability to concentrate, sometimes raising fears about their own capacity to cope.¹⁷ Taking that seriously, asking for help, sharing nighttime duties, and sleeping when the baby sleeps, is not a luxury but a practical necessity for staying well during a genuinely demanding period.