Babies who were sleeping through the night often start waking again, and it almost always traces back to something specific: a developmental leap, a growth spurt, physical discomfort, or a shift in their daytime schedule. This is so common it has a name (sleep regression), and it’s temporary. Understanding what’s driving the change helps you respond in the right way and get back to longer stretches of sleep faster.
Sleep Regressions Are Tied to Development, Not Age
You’ll see lists online pinning sleep regressions to exact ages (4 months, 8 months, 12 months), but regressions are less about a baby’s age and more about what they’re going through at any given time. A baby who just learned to roll over or pull to standing may wake repeatedly because their brain is buzzing with the new skill and they want to practice it, even at 2 a.m. The classic pattern of shifting from deep, predictable sleep to lighter, more disrupted cycles usually shows up around four months, when a baby’s sleep architecture matures to resemble adult-like sleep stages for the first time. Before that point, newborns cycle through sleep differently, which is why the four-month mark often feels like the first real regression.
After four months, regressions tend to cluster around major milestones: crawling, cruising, first words. Each new skill temporarily reorganizes how your baby’s brain handles sleep. These phases typically last one to three weeks if nothing else is reinforcing the waking.
Growth Spurts and Hunger
Growth spurts are one of the most straightforward explanations for sudden night waking. Typical infant growth spurts happen at 2 to 3 weeks, 6 weeks, 3 months, 6 months, and 9 months. During a spurt, your baby’s caloric needs jump, and a feeding schedule that was perfectly adequate last week may leave them genuinely hungry at night. You’ll often notice increased daytime appetite at the same time.
If your baby is around six months and you haven’t started solids yet, that could also play a role. A large study from King’s College London found that babies introduced to solid foods earlier slept about 16 minutes longer per night and woke less frequently, with differences peaking at six months. That’s nearly two extra hours of sleep per week. Sixteen minutes may sound small, but the reduction in wake-ups is what parents actually feel. If your baby is developmentally ready for solids and waking hungry, adding calories during the day can make a noticeable difference at night.
Separation Anxiety Peaks Around 9 Months
If your baby is between 9 and 18 months and suddenly can’t let you leave the room without crying, separation anxiety is the likely culprit. This is a completely normal developmental phase. Your baby now understands that you exist when you’re out of sight but doesn’t yet trust that you’ll come back. At night, that translates to waking up, realizing they’re alone, and calling for you.
The instinct is to change everything to soothe them, but consistency matters most here. Brief reassurance visits without picking your baby up or turning on lights signal that you’re nearby without creating new sleep associations that extend the problem. Separation anxiety fades on its own over the following weeks and months.
Teething Pain Is Real but Short-Lived
Teething gets blamed for almost every sleep disruption in the first two years, but the actual window of discomfort from any single tooth is about eight days. Symptoms like drooling, irritability, and disrupted sleep tend to begin roughly four days before the tooth breaks through the gum and continue for about three days after. If your baby has been sleeping poorly for weeks and you’re attributing it to teething, something else is probably going on too.
The teeth most likely to cause noticeable pain are the molars, which arrive later (typically 13 to 19 months for the first set). Front teeth breaking through rarely cause the kind of pain that wakes a baby repeatedly. If you suspect teething, look for swollen gums and excessive drooling during the day as confirmation.
Their Daytime Schedule May Need Adjusting
A baby who’s undertired or overtired at bedtime will wake more at night. Both problems look similar from the outside, but the fix is different. The key variable is wake windows: the stretches of time your baby stays awake between naps. These expand as babies grow, and if you’re still following a schedule that worked two months ago, it may no longer fit.
General wake window ranges by age:
- 3 to 4 months: 1.25 to 2.5 hours
- 5 to 7 months: 2 to 4 hours
- 7 to 10 months: 2.5 to 4.5 hours
- 10 to 12 months: 3 to 6 hours
If your baby is between 6.5 and 8 months and suddenly fighting naps, waking at night, or needing a bedtime pushed past 8 p.m. to squeeze in a third nap, they’re probably ready to drop from three naps to two. Signs that a nap transition is overdue include protesting or refusing one of their naps, waking before 6 a.m. when they previously didn’t, and short naps across the board. Dropping the third nap and stretching the remaining two usually resolves the nighttime waking within a week or so.
Room Temperature and Sleep Environment
Babies wake when they’re too warm more often than when they’re too cold. The recommended room temperature for infant sleep is 16 to 20°C (roughly 61 to 68°F). A room above that range, especially combined with heavy pajamas or blankets, can cause restless sleep, sweating, and frequent waking. If your baby’s chest or back feels damp or hot when you check on them, the room is too warm.
Light bedding or a well-fitting sleep sack is enough for most rooms within that temperature range. Keeping the room within 16 to 20°C also lowers the risk of SIDS, so it’s worth checking even if you don’t think temperature is the primary issue.
Illness and Ear Infections
A cold, ear infection, or any illness that causes congestion or pain will disrupt sleep abruptly. This is usually easy to identify because it comes with other symptoms: fever, runny nose, pulling at ears, or general fussiness during the day too. The sleep disruption resolves when the illness does, though it can take a few extra nights for your baby to settle back into their previous pattern afterward.
If your baby snores regularly, breathes through their mouth during sleep, or has pauses in breathing followed by gasping or choking, that’s worth a conversation with your pediatrician. These are symptoms of obstructive sleep apnea, which is different from a temporary cold. Nighttime sweating and restless sleep are other signs. During the day, children with sleep apnea may breathe through their mouth or complain of morning headaches once they’re old enough to communicate that.
What Actually Helps
The most effective thing you can do is identify which category your baby’s waking falls into, because the response differs. A hungry baby during a growth spurt needs an extra feeding. A teething baby needs comfort for a few days. A baby whose schedule is off needs a nap adjustment, not more nighttime soothing. Responding to every waking the same way, especially by adding new sleep associations like rocking to sleep or bringing the baby into your bed, can turn a two-week regression into a months-long habit.
Keep the environment consistent: dark room, white noise if you use it, same sleep location. When you do respond to waking, keep interactions brief and boring. Low light, quiet voice, minimal stimulation. The goal is to address the underlying need (hunger, pain, reassurance) without signaling that nighttime is an interesting time to be awake.
Most regressions resolve within two to four weeks. If your baby’s sleep has been disrupted for longer than that with no clear cause, or if you’re seeing symptoms like snoring, gasping, or pauses in breathing, it’s worth getting a professional evaluation to rule out something physical.