Why Does My Newborn Laugh in His Sleep? The Science Explained

As a child psychiatrist specializing in newborn behavior for over four decades, one of the most common questions I get from bleary-eyed new parents is, "My baby was laughing in his sleep! What does that mean?" The first time you see your newborn giggle while fast asleep, it's a magical moment, but it can also be a bit mystifying. Let me reassure you: as of 2025, our understanding confirms this is almost always a perfectly normal, and fascinating, part of early development (learn more). Knowing the science behind these cute sleep sounds can help you appreciate this milestone and understand the remarkable things happening in your baby’s brain.

The Science Behind Newborn Sleep Cycles

Newborn sleep is very different from adult sleep. While we adults spend about a quarter of our sleep in the REM (Rapid Eye Movement) stage, newborns can spend up to half their sleep time there. This is their "active sleep" phase. During REM sleep, your baby's brain is buzzing with activity, processing information, building connections, and their eyes are darting around beneath their eyelids. It's a busy time in there! This is the prime time for sleep laughter. Essentially, their brain gets a jolt of stimulation while their body is still resting, which can trigger involuntary facial movements and sounds that look and sound just like a laugh.

Understanding Endogenous Smiles and Primitive Reflexes

The smiles and laughs you see during sleep are what we in the field call "endogenous smiles" and "primitive reflexes." Simply put, these are expressions that come from within the brain, not in response to you telling a joke. They are spontaneous and can be seen right from the neonatal period.

What Are Endogenous Smiles?

• Generated internally by spontaneous brain activity
• Not a reaction to the environment
• Considered harmless and physiological
• Observable from birth

Primitive Reflexes Explained

These behaviors are automatic, not conscious or social. They come from deep-seated parts of the brain, including the brainstem and limbic system (hypothalamus and amygdala).

Unlike the social smile that will melt your heart in a few weeks, these reflexes are a sign that the nervous system is maturing properly and a good indicator of healthy early neural development.

Six Main Reasons Newborns Laugh in Their Sleep

1. Active Brain Development During REM Sleep

During active sleep, your baby's brain is hard at work processing information and forming important neural connections. This intense brain activity can trigger involuntary facial expressions, including what looks like laughter. You can imagine it as little sparks of electricity firing in the brain, occasionally hitting the muscles that make a smile or a laugh.

2. Primitive Reflexes at Work

Newborns have many involuntary reflexes that don't depend on feelings or deliberate thought. These built-in reflexes can create sounds and faces that seem like laughter during sleep. Just as babies practice smiling in the womb, these sleep expressions are automatic, not emotional.

3. Practicing Social and Emotional Skills

I like to think of sleep laughter as practice for the big show. This neural rehearsal helps build the foundation for future social skills. It's the brain getting ready for all the smiling and laughing your baby will do when they are awake and interacting with you.

4. Facial Muscle Development

These sleep expressions also give the facial muscles a good workout. This helps strengthen them and fine-tune the brain pathways needed for communication later on. This spontaneous activity prepares the coordination needed for more complex social expressions as your baby grows.

5. Processing Sensory Experiences

While asleep, babies process the sensory experiences from their day. Their "dreams" aren't complex stories but more like simple sensory replays, the feeling of being held, the sound of a parent's voice. Sometimes, processing these pleasant sensations might trigger a happy response, like a giggle.

6. Brain Maturation Indicator

Ultimately, sleep laughter is a harmless and positive sign that the brain is maturing and that the capacity for social interaction is developing just as it should.

How Sleep Laughter Differs from Other Sleep Behaviors

Sleep laughter is one of several common behaviors you might notice while your baby is in the active (REM) sleep phase:

All of these are typically harmless and point to normal neurological and physical development.

Distinguishing Normal Sleep Laughter from Concerning Signs

Normal Newborn Sleep Laughter:

Sound Characteristics:

• Gentle and soft
• Spontaneous and joyful
• Similar to baby's regular happy laugh
• Fits the context of peaceful rest

Duration and Frequency:

• Brief episodes (few seconds)
• Occasional occurrence
• Not clustered or repetitive

Physical Movements:

• Gentle facial movements
• Soft body twitches typical of REM sleep
• Baby remains peaceful
• Quickly returns to sleep

Warning Signs – Gelastic Seizure (Rare):

Sound Characteristics:

• Unnatural or forced quality
• Hollow or mechanical sound
• Abrupt or "machine-like"
• Out of place during rest

Duration and Frequency:

• Lasts 10-30 seconds
• Stops abruptly
• High frequency (multiple times daily)
• Occurs in clusters at random times

Physical Movements:

• Vacant or staring spells
• Sudden grunting or squirming
• Facial flushing
• Repetitive movements (lip smacking, fidgeting)
• Eye or head deviation
• Confusion or tiredness following episodes

If you see any of these warning signs, laughter that sounds forced, lasts longer than a few seconds, happens very often, or comes with unusual body movements, it’s time for a check-up. I always tell parents to trust their gut; if something feels off, bringing it up with your pediatrician is the right move.

What Sleep Laughter is NOT Related To

A common question I hear is whether a baby laughing in their sleep is just passing gas. It’s a funny thought, but there is no scientific evidence connecting sleep laughter to digestive functions like passing gas, bowel movements, or acid reflux. The key difference is comfort. A baby with gas is usually showing signs of discomfort, straining, grunting, or crying. Sleep laughter happens when they are peaceful. Laughing in their sleep is tied to brain activity, not tummy activity. For another parent-friendly explanation, you can check out this guide on WonderBaby (read more).

What Parents Can Expect as Baby Grows

This sleepy giggling phase doesn't last forever. Here’s a general timeline for how this behavior changes as your baby grows:

Birth to 6-8 weeks:

• Sleep smiles and giggles appear from birth
• Involuntary expressions dominate

6-8 weeks:

• Voluntary social smiles typically emerge during wakefulness
• The transition from reflex to communicative acts begins

3-4 months:

• Sleep patterns become more organized
• Sleep expressions may decrease
• Social laughter during wakefulness develops (typically 3-4 months)

Beyond 4 months:

• Babies gradually spend less time in REM sleep, so sleep laughter often decreases naturally. However, some babies will continue to chuckle in their sleep well into infancy. It’s all part of their unique development.

Supporting Your Baby's Healthy Sleep Development

While sleep laughter doesn't need any 'fixing,' you can support your baby's overall sleep health with a few simple practices:

• Create a consistent sleep environment with suitable lighting and noise levels
• Recognize that newborns typically sleep 14-17 hours daily, but in short cycles
• Learn your baby's sleep cues (eye rubbing, yawning) to help them sleep before overtiredness
• Avoid waking a laughing baby. It's tempting to share in the joy, but as I've mentioned, that sleep is when their brain is doing some of its most important work.

Common Myths About Newborn Sleep Laughter

Conclusion

So, that little giggle from the bassinet is a wonderful peek into the complex development happening inside your newborn's brain. These early smiles and laughs are not just random reflexes; they are the building blocks for future communication and connection. From my perspective, the shift from these automatic sleep expressions to a deliberate, social smile is one of the most incredible milestones of infancy. The next time you hear your newborn chuckle in their sleep, you'll know it's a sign of healthy growth. You're witnessing their brain preparing for a lifetime of shared smiles and laughter with you.

Frequently Asked Questions

Is it normal for newborns to laugh in their sleep?

Yes, it's completely normal. Sleep laughter typically occurs during REM (active) sleep when the brain is highly active. These are endogenous smiles and primitive reflexes that are a sign of healthy brain development.

When do babies start laughing while awake?

While sleep laughter can occur from birth as an involuntary reflex, social laughter during wakefulness typically emerges around 3-4 months of age, after social smiling has developed (usually at 6-8 weeks).

Should I wake my baby when they laugh in their sleep?

No, it's best not to wake your baby. These moments of sleep laughter are part of normal brain development and sleep cycles. Interrupting them isn't necessary and may disrupt important neural development.

When should I be concerned about my baby's sleep laughter?

Consult your pediatrician if you notice forced or mechanical-sounding laughter lasting 10-30 seconds, high frequency episodes, accompanying staring spells, unusual body movements, or if the laughter seems clearly different from normal happy sounds.

Is sleep laughter related to digestive issues?

No scientific evidence links newborn sleep laughter to digestive processes like gas, bowel movements, or acid reflux. Digestive issues typically cause discomfort and disrupt sleep, while sleep laughter occurs during peaceful rest.

Further Reading and References

For more information and further reading on infant sleep and development, consider these authoritative sources:

• American Academy of Pediatrics (AAP): https://www.aap.org/
• Healthline on Laughing in Sleep: https://www.healthline.com/health/laughing-in-sleep
• Sleep Foundation – Why Do Babies Smile in Their Sleep: https://www.sleepfoundation.org/baby-sleep/why-do-babies-smile-in-their-sleep
• Huckleberry Care – Why Does Your Baby Laugh and Smile in Sleep: https://huckleberrycare.com/blog/why-does-your-baby-laugh-and-smile-in-sleep
• Omega Pediatrics – Why Newborn Baby Smile While Sleeping: https://www.omegapediatrics.com/why-newborn-baby-smile-while-sleeping/