Sudden nighttime crying in a baby who previously slept well is almost always tied to a temporary change: a developmental leap, a growth spurt, teething, separation anxiety, or the early signs of illness. Most of these causes resolve on their own within a few days to a couple of weeks. The key is figuring out which one you’re dealing with so you can respond in a way that helps your baby (and you) get back to sleep.
Sleep Regressions and Changing Sleep Patterns
Babies go through roughly six stages of sleep regression, commonly around 4, 6, 8, 12, 18, and 24 months. These aren’t random setbacks. They reflect real changes happening in your baby’s brain. At 4 months, for example, your baby’s sleep architecture starts shifting from infant-style sleep toward more adult-like cycles with distinct stages of light and deep sleep. That transition is a good thing long-term, but in the short term it means more partial awakenings and more opportunities for crying.
A baby’s sleep cycle lasts only about 45 to 60 minutes, compared to 90 minutes for adults. Every time a cycle ends, your baby briefly surfaces toward wakefulness. Before the regression, they may have drifted back to sleep without you noticing. Now, as their brain reorganizes how it handles sleep, those between-cycle moments become fully awake, fully crying moments. This typically lasts one to three weeks.
Growth Spurts and Hunger
Growth spurts tend to happen around 2 to 3 weeks, 6 weeks, 3 months, and 6 months, though every baby’s timing is different. During a spurt, your baby needs more calories than usual, and nighttime hunger can wake them even if they’d been sleeping through. The crying often sounds urgent and calms quickly once they’re fed. Growth spurts usually last only a few days, so if increased feeding settles the crying, this is likely your answer.
Teething Pain
Teething can start as early as 3 months and continue through age 3, so it overlaps with nearly every other possible cause on this list. The earliest signs are heavy drooling and your baby pressing anything they can find against their gums. Pain from an emerging tooth tends to be worse at night because there are fewer distractions, and lying down can increase pressure in the gums.
A teething baby may run a low-grade temperature under 101°F, but anything higher, especially combined with a runny nose or diarrhea, is more likely a virus than teething. If the crying seems tied to chewing behavior during the day and your baby is in the typical age range for new teeth, a chilled teething ring before bed can help take the edge off.
Separation Anxiety
Between about 8 and 12 months, babies develop a much stronger sense of object permanence: they now understand that you still exist when you leave the room. That’s a cognitive milestone, but it also means bedtime feels like a real separation. Your baby may refuse to let you put them down and then wake in the middle of the night searching for you.
Separation anxiety peaks between 10 and 18 months and gradually fades during the second half of the second year. During this phase, your baby isn’t being manipulative. They genuinely feel distressed when they can’t see or feel you. Brief, calm reassurances when they wake, without turning it into extended playtime, help them learn that you’re still nearby even when they can’t see you.
Developmental Milestones
Learning to roll, crawl, or pull to standing can temporarily disrupt sleep. Babies often “practice” new motor skills in their crib, sometimes waking themselves up in the process. A baby who has just learned to pull up, for instance, may stand in the crib and then cry because they haven’t figured out how to sit back down. This kind of disruption is brief and resolves once the new skill becomes routine, usually within a week or two.
Illness or Ear Infection
If the crying came on very suddenly and your baby seems different during the day too, illness is worth considering. Ear infections are a common culprit because the pain intensifies when a baby lies flat. Signs to watch for include tugging or pulling at the ears, fever, fluid draining from the ear, trouble with balance, and not responding to quiet sounds. A baby with an ear infection will often seem more uncomfortable when you lay them down than when you hold them upright.
Colds, stomach bugs, and urinary tract infections can also cause nighttime crying that seems to come out of nowhere. The distinguishing factor is usually that illness-related crying doesn’t follow a pattern. It’s not just at bedtime or during transitions between sleep cycles. It’s persistent, and your baby seems uncomfortable or “off” during waking hours as well.
Overtiredness
This one is counterintuitive: a baby who hasn’t slept enough during the day often sleeps worse at night, not better. When your baby becomes overtired, their stress response kicks in, flooding their body with cortisol and adrenaline. Cortisol disrupts the sleep-wake cycle, and adrenaline triggers a fight-or-flight state that makes it genuinely harder for them to fall and stay asleep. The result is a wired, fussy baby who cries more at night despite being exhausted.
If your baby’s daytime naps were shorter than usual, or if bedtime got pushed later, overtiredness may be driving the sudden nighttime crying. Moving bedtime earlier by even 15 to 30 minutes can sometimes break the cycle within a night or two.
How to Respond Without Making It Worse
Whatever the cause, how you handle nighttime crying matters for how quickly things return to normal. The goal is to comfort your baby without turning the middle of the night into something stimulating or interesting. Keep the room dark, your voice low and soothing, and avoid playing or making eye contact that signals “time to be awake.” If you share nighttime duties with a partner, use the same approach so your baby gets a consistent message.
Putting your baby down drowsy but still awake, rather than fully asleep in your arms, helps them practice the skill of falling asleep independently. That skill is what eventually gets them through those between-cycle awakenings without needing you. This doesn’t mean ignoring their cries. It means giving them a brief chance to settle before stepping in, and keeping your interventions calm and boring when you do.
Most causes of sudden nighttime crying are self-limiting. Growth spurts pass in days. Sleep regressions resolve in one to three weeks. Teething pain comes and goes as each tooth moves. If the crying persists beyond two to three weeks, gets worse over time, or comes with signs of illness like high fever or changes in eating, that’s worth a call to your pediatrician to rule out something that needs treatment.