Why Do Babies Smile in their Sleep?

Is there anything more peaceful and heartwarming than watching your baby smile when sleeping? I would often wonder what’s going on in their heads when this happens. “Are they having a good dream?”  I’d ask myself. “Are they playing with angels?”  

Even though there is not a great amount of scientific evidence regarding the cause, different experts have potential explanations as to why infants smile in their sleep.  

3 Types of Smiles in Infants 

Before we dive into the reasons why our little bundles of joy smile in their sleep, let’s talk about the three different types of smiles:

  • Social 
  • Reflexive 
  • Responsive 

Social smiles happen when babies can independently express their own emotions. These smiles usually occur when babies are between the ages of 3 and 4 months old. Social smiling only emerges when our babies are fully attentive to their surroundings. Therefore, babies don’t smile in their sleep to express their own emotions. 

Reflexive smiles are smiles that do not happen in response to changes outside of the body. These smiles happen during the month after our little ones enter the world. They have little to do with emotion and more to do with our babies’ instinct to begin practicing different skills. 

Responsive smiles happen when sounds and movements occur outside of our babies’ bodies. For example, if we talk to our babies in a soft and gentle tone while their little eyes are closed, they can respond by smiling. 

REM Sleep

Whether or not our babies can dream, it is up for debate in the scientific community. Many scientific experts believe that babies cannot dream because their experiences are limited, and their brains are not mature enough to process dreams.

However, babies do experience REM (Rapid Eye Movement) sleep, which is when dreams occur. According to the Children’s Hospital of Philadelphia, before babies enter REM sleep, they must go through a process of sleep that contains four stages.

4 Stages of Sleep

  • Stage 1: Babies experience drowsiness, and their eyes open and close.
  • Stage 2: Babies go into a light sleep and might be startled by sounds and movements.
  • Stage 3: Babies enter deep sleep.
  • Stage 4: Babies enter profound sleep.

Babies start in stage 1 and continue to stage 4. They then go back to steps 3 and 2, and finally to REM. It is common to see babies make involuntary movements and sounds during REM, such as jerking, jumping, smiling, laughing, whimpering, and crying. 

Babies Learn While They Sleep

Another reason why babies smile in their sleep is that they are learning about their new environment. 

In the 2010 research article, Newborn infants learn during sleep, scientists monitored bioelectrical activity in 34 healthy newborns by placing electrodes on their faces and scalps. 

To track whether the babies could sense sound and touch while they were sleeping, researchers provided different tones through two speakers and used a flexible tube that delivered a puff of air to the outer corner of babies’ right eye. It turns out that the babies were quick to learn the predictive relationship between the tone and the puff of air. 

Therefore, when our babies take a snooze, movements such as eye movement and smiling are signs that they process information. Babies can process structural aspects of language while they sleep. Even when our babies were in our wombs, they could learn about the structural elements of speech from hearing our voices. 

Medical Causes

In healthy babies, smiling while taking a snooze is usually expected. However, Healthline says that gelastic seizures can occur in babies in rare cases, causing episodes of uncontrolled laughing. This type of epilepsy can last around 10 to 20 seconds, and symptoms are present when babies are ten months old. 

If your baby’s uncontrolled laughing is accompanied by grunting, blank stares, and squirming, you must seek medical attention as soon as possible. Since diagnosing gelastic seizures can be difficult, you must make sure to provide detailed information to the pediatrician so that he or she can conduct the right kind of tests to see what’s happening with your infant.

In Closing

As a mom, watching my baby smile while sleeping is a very adorable and memorable phenomenon to behold. Even though there is still more research to do on why babies smile in their sleep, at least we know that it is a sign that our babies are growing, developing, and learning about their environment. 

I hope that I have given you some information surrounding the reasons behind the blessing of your baby smiling in their sleep. Enjoy watching the beautiful process of your baby growing into a healthy human being.  

Scroll to Top