Why Do Babies Laugh in Their Sleep?

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Babies often smile and laugh in their sleep. This behavior is extremely cute, but the reasons why is the subject of scientific debate with no real conclusion.

In this article, we will look at the arguments for why could cause these cheeky little smiles and try to understand the science of baby sleep, laughing, and smiles in general.

This will help new parents understand more about what could be happening internally with their newborn baby.

when babies laugh in their sleep

The Cause of a Baby Laughing in their Sleep

Do Babies Dream?

If a baby is laughing in their sleep then surely they must be dreaming right?

Unfortunately, there is no definitive proof that babies dream because… well, they cannot speak.

But, there are scientific arguments that go both ways.

The Argument Against Baby Dreaming

According to psychologist David Foulkes – an expert on pediatric dreaming – babies do not dream.

In an interview with Live Science magazine, he stated that just because something perceives reality does not mean they can dream one, regardless of what we may think.

A newborn baby has very limited experience and their brains are not mature enough to work this way at such a young age.

The Argument for Baby Dreaming

On the other hand, Dr. Charles Pollak of the Sleep Center for Medicine in New York argues that because babies experience rapid eye movement (REM) – the stage of sleep in which dreams occur) the physical signs suggest active dreaming.

Whether or not babies truly dream is something that has yet to be proven. Because of this, we cannot draw the conclusion that they are laughing at something they see in their dreams.

Instead, to gain a bit more insight into what is behind this phenomenon, let us explore the subjects of sleep cycles and smile development.

About Baby Sleep Cycles

Have you ever felt like the same moment your head hit the pillow at night to sleep, it was morning, and time for you to start a new day?

You probably felt like you slept straight through the night, undisturbed, in an even state (OK, maybe you do not remember, since it was like a year ago, before pregnancy and baby).

The truth is we all go through sleep cycles throughout the night, whether we realize it or not. We drift back and forth between shallow and deep sleep, and there are even some who are fortunate to never fully wake until morning (how I wish this was me…).

Babies are the same way, constantly drifting through sleep cycles, although much more quickly than we do as adults.

They may experience a repeated sleep cycle 7 to 9 times throughout the night and about 3 times during a nap, each lasting only about 20 to 40 minutes for a newborn and 30 to 60 minutes for an infant (adults typically go about 90 minutes between sleep cycles).

Sleep cycles are made up of different stages, repeated in a certain sequence, unique to each person (such as: awake, 1, 2, 3, 4, 3, 2, REM).

These stages are characterized by different factors and may give us a better idea of what we are seeing as we watch our sleeping angel:


Non-REM Sleep (Stage 1)

Non-REM sleep can also be called light or shallow sleep, and stage 1 is the first step between awake and asleep.

Our bodies begin to relax and breathing becomes more regular, but we can still be easily woken by the slightest movement or sound.

Non-REM Sleep (Stage 2)

This stage is the first of official “light” sleep. The heart rate begins to grow slow and steady, and body temperature begins to drop.

For some of us, especially babies, we may slightly twitch or grunt during this stage of non-rem sleep as well.

Non-REM Sleep (Stage 3 & 4)

There is not much physical difference between stages 3 and 4 of non-REM sleep. Only when brain activity is measured on a polygraph can you tell the difference.

The body is completely relaxed, and if roused by a sudden movement or sound, you would likely react slowly and drift back to sleep.

REM Sleep

This is the stage we need to arrive at in our sleep, as it is important for both babies and adults. Even though it takes our bodies a while to reach this stage, it is, actually, very light and we can be easily woken.

It is also the most active. This is where dreams occur in adults, and because babies reach this level of sleep as well, it can be argued that, perhaps, they have dreams too.

This stage is crucial, with increased blood flow to the brain which helps our brains to grow as children and our bodies to repair as adults. Growth hormones are also secreted at this stage, which is why your baby may sleep more when she is going through a growth spurt.

Rapid Eye Movement sleep is characterized by increased heart rate and breathing, which can cause your baby’s body to have involuntary movements.

Her eyes will probably be moving a lot, and her face, fingers, and legs may twitch.

It is during REM sleep that we often see babies smile and laugh.

Since adults dream at the REM sleep stage, we can hypothesize the same for babies.

However, these laughs and smiles may just be involuntary twitches thanks to REM sleep, just like those moving eyes and kicking legs.

Babies Smile

There are several classifications of baby smiles that could be more reflexive than based on an internal sense of well-being.

These vary depending on a child’s developmental stage and their capability to make a conscious smile.


Reflexive Smile

Typically, between the ages of 0 to 1 month, babies are unable to consciously smile in reaction to something they see.

There may be little mouth twitches that can be classified as smiles, little sounds that could be laughs, but there is no emotional connection in them.

These are the smiles and laughs you likely see during REM sleep that makes you think your little one may be having a nice dream.

In reality, it is probably just another reflex that their bodies are practicing in preparation for the real thing.

Reactive Smile

This is where things start to get a little more fun. Your baby, around the age of 2 months, can start reacting to things she likes with a smile or laugh.

I will never forget that first smile I saw on my daughter’s face, as she smiled at the picture I painted for her before she was born.

At this stage, smiles and laughs may still be few and far between. Your baby is just reacting to her environment, which helps you understand her a bit more as she is signaling what she finds enjoyable, but these smiles are still different from smiling socially.

Social Smile

Social smiles start around 3 to 4 months of age. They may still seem like reactive smiles in some ways, as she is showing excitement for something she likes, but the difference here is that when she smiles at you, she is truly starting to connect.

When your baby is connecting with you and her environment, she is truly showing happiness.

She knows why she is smiling, exhibiting this by the duration of her smile, and she may even try to get your attention by smiling.

Gas Smile

Sometimes grouped with reactive smiles, gas smiles are exactly what they sound like: the involuntary facial expression showing relief from the release of unwanted tummy gas.

These can also occur during sleep, making it look like your baby is laughing or smiling in a dream.

Final Word

Research can only tell us so much about why a baby laughs and smiles while sleeping. So we cannot reach a definitive conclusion to this article except to better understand the stages of non-rem, and rem sleep that may be triggering these reactions.

Personally, I would like to believe that babies dream during REM sleep. Their brain waves would be on overdrive as they discover this new world around them and is sure to make for some interesting dreams.

But regardless of where the truth lies, a baby laughing in sleep makes them look happy and this must surely be a good thing.

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