Baby Won't Sleep at Night: Common Causes and What to Try

If your baby is wide awake at 2am while the rest of the world sleeps, you are not alone. Night-time sleep problems are one of the most common reasons parents seek help, and the frustration is completely understandable. You are exhausted, your baby seems wired, and nothing you try seems to make a difference.

The first thing to know is that the reason your baby is not sleeping at night depends almost entirely on their age. A newborn who will not sleep at night is dealing with something fundamentally different from a 9-month-old who wakes every hour. And a toddler who fights bedtime for 90 minutes has different things going on again.

Understanding the most likely cause for your baby's age is the starting point. Not because it gives you a quick fix, but because it helps you stop blaming yourself and start looking in the right direction. In almost every case, a baby who will not sleep at night is not being difficult. Something specific is driving the waking, and once you know what it is, you can start to address it.

This guide walks through the most common causes by age group, the environmental factors that affect every baby regardless of age, and the signs that something medical might be going on.

If your newborn sleeps beautifully during the day and is wide awake all night, this is almost certainly day-night confusion, and it is completely normal. Your baby is not being awkward. Their circadian rhythm simply has not developed yet.

In the womb, your baby had no concept of day and night. They slept and woke in their own rhythm, often most active in the evening and at night (which you probably remember from pregnancy). After birth, it takes around 6 to 12 weeks for the circadian rhythm to establish, and during that time, many newborns have their longest sleep stretches during the day and their most wakeful periods at night.

Light exposure is the single biggest factor in helping the circadian rhythm develop. Daylight tells your baby's brain "this is daytime," and darkness signals "this is night time." Natural light during the day, particularly morning light, helps set the internal clock. Keeping things dim and quiet at night reinforces the message.

Feeding patterns also play a role. Newborns need to feed frequently, typically every 2 to 3 hours, and this is true day and night. Night feeds are normal and necessary at this age. The goal is not to eliminate night feeds but to help your baby gradually start to consolidate their longer sleep stretches into the night-time hours. For a more detailed look at this stage, our newborn sleep guide covers it thoroughly.

Between 3 and 6 months, the most common reason a baby will not settle or stay asleep at night is sleep associations. A sleep association is anything your baby has learned to need in order to fall asleep, and then needs again every time they wake between sleep cycles during the night.

At around 4 months, your baby's sleep cycles mature from two stages to four, which means they have more partial arousals during the night. Every time they surface between cycles, roughly every 45 minutes to 2 hours, they check whether the conditions are the same as when they fell asleep. If something has changed, they wake fully and signal for help.

The most common sleep associations at this age include being fed to sleep, being rocked or bounced to sleep, being held until deeply asleep, and the dummy falling out. None of these are bad things. Feeding to sleep is biologically normal and is only a problem if it is unsustainable for your family. But if your baby falls asleep in your arms and wakes up in the cot, from their perspective, something has changed, and that mismatch is what drives the frequent waking.

This period also coincides with the 4-month sleep regression, which is a permanent change in sleep architecture rather than a phase. If your baby's sleep fell apart around 4 months and has not recovered, sleep associations are very likely the reason.

From 6 months onwards, the picture gets more complex because multiple factors can overlap. Separation anxiety typically emerges between 6 and 10 months as your baby develops object permanence, the understanding that you still exist when you leave the room. This can cause intense bedtime resistance and frequent night waking.

Teething is often blamed for sleep disruption in this age range, and while it can cause 1 to 3 days of discomfort around each tooth, it rarely explains weeks of persistent waking. If your baby's sleep has been disrupted for more than a few days, something else is likely contributing.

Motor milestones also play a significant role. Babies learning to crawl, pull to stand, or cruise often practise these skills during sleep, waking themselves up in the process. Finding your baby standing in their cot at 3am, crying because they cannot get back down, is a classic feature of this period.

Schedule issues can emerge here too. If your baby is getting too much daytime sleep, or their nap timing is off, it can directly affect how well they sleep at night. An overtired baby who has missed their sleep window can be just as hard to settle as an undertired baby who simply is not tired enough for bed. Our guide on overtired vs undertired babies covers how to spot the difference.

Once your baby passes their first birthday, the reasons for not sleeping at night shift again. While separation anxiety can still be a factor (it often peaks again around 18 months), schedule issues and boundary-testing become increasingly common.

Many toddlers fight bedtime not because they are not tired, but because they do not want to stop being awake. The world is interesting, they have opinions about it, and going to sleep means missing out. This is developmentally normal. Toddlers are wired for exploration and autonomy, and bedtime is the opposite of both.

Nap transitions also create night-time disruption. Moving from two naps to one, which typically happens between 14 and 18 months, can temporarily throw off the whole schedule. Too much daytime sleep steals from night sleep. Too little daytime sleep creates overtiredness, which makes bedtime harder and night waking more likely.

Night terrors and nightmares can also emerge in the toddler years. Night terrors are partial arousals from deep sleep where your child appears distressed but is not actually awake. Nightmares happen during lighter sleep and your child will be genuinely upset and awake. Both can disrupt the night but have different causes and different approaches.

If your toddler's sleep has been consistently poor, it is worth looking at the whole picture: the daytime schedule, the bedtime routine, the sleep environment, and whether there are any underlying factors like illness or discomfort that need addressing first.

Regardless of your baby's age, the sleep environment plays a significant role in how well they settle and stay asleep. These are the foundations that apply across the board.

Light. Darkness triggers melatonin production, which helps your baby feel sleepy. Even small amounts of light, including standby lights on monitors, light creeping around blinds, or a night light that is too bright, can interfere with this process. A properly dark room makes a measurable difference. Our sleep environment guide goes into detail on this.

Temperature. The Lullaby Trust recommends a room temperature between 16 and 20 degrees. Overheating is a risk factor for SIDS, and a room that is too warm can also cause restless sleep and more frequent waking. Check the back of your baby's neck rather than their hands or feet to gauge temperature. See our temperature guide for more.

Noise. Consistent, low-level white noise can help mask household sounds and create a consistent sleep cue. The key word is consistent. Turning it off after your baby falls asleep changes the environment, which can cause waking when they surface between sleep cycles.

The cot itself. A firm, flat mattress with a fitted sheet and nothing else. No pillows, toys, bumpers, or loose blankets for babies under 12 months. The Lullaby Trust recommends room sharing for the first six months, with the baby in their own cot or Moses basket in the same room as you.

Most babies who will not sleep at night have a behavioural or developmental explanation. But sometimes, there is a medical cause that needs investigating. It is important to know the difference, because no amount of routine adjustment will fix a problem that has a medical root.

Signs to discuss with your GP or health visitor:

• Breathing changes during sleep. Pauses in breathing, gasping, persistent snoring, or noisy breathing are always worth investigating.
• Persistent arching of the back, especially during or after feeds. This can indicate reflux or a food intolerance.
• Frequent vomiting or bringing up large amounts of milk. Occasional spit-up is normal, but frequent, forceful vomiting is not.
• Refusing feeds or poor weight gain. Feeding difficulties that affect weight are a medical concern.
• Persistent rashes or digestive discomfort after starting solids. This could suggest a food allergy or intolerance.
• Extreme, inconsolable crying that is different from their normal unsettled behaviour. If your instinct says something is wrong, trust it.

If you are worried about your baby's health, speak to your GP or health visitor. Sleep consultants can help with the behavioural and environmental side of sleep, but anything that might have a medical cause needs to go through a medical professional first. Once any medical issues are addressed, the sleep side can be supported alongside.

There is no single answer to "why won't my baby sleep at night" because every baby, every age, and every family situation is different. The general principles, age-appropriate expectations, and environmental foundations apply broadly. But the specific combination of factors affecting your baby's sleep, and what to try first, is individual. That is where personalised support makes the biggest difference.