Why Do Babies Smile in Their Sleep?

Why Do Babies Smile in Their Sleep?

Is your newborn smiling at you? Many new parents will fall in love over and over again when they see a little smile begin to form on their newborn’s face. Many times, these smiles occur when the baby is sleeping, but for any new parent a smile from their baby is priceless!  However, the question for many parents remains, why do very young babies smile in their sleep? Well, there could be several reasons for those adorable smiles.


Newborn babies are born with several reflexes that actually begin to develop while the baby is still developing in utero. Among these reflexes are newborn smiles. Like many newborn reflexes, smiles are a way for the baby to practice using their muscles. In essence, this is Mother Nature’s way to make sure that the different parts of the baby’s body are in working order. Reflexive smiling happens from before birth to around 2 months of age. Once the baby gets closer to 3 months of age, they will begin to become more interactive with their caregivers and we will start to see a different type of smile begin to emerge in response to seeing their parents or others who engage with them in a loving or positive way.  

Gastrointestinal Sensations

Sometimes, when your little one is sleeping they will also begin to experience sensations in their belly that feel strange to them. The process of digestion, and the gas that may go along with it can also be a cause for facial expressions including smiling. You probably notice many different ways that your baby moves their face during sleep - these grimaces, frowns, and smiles can all be in response to the digestive system making them feel like they need to release some emotions along with the gas! Think of it this way, in utero, a baby’s body doesn’t need to do any of the work that goes along with feeding and emptying their bowels. The umbilical cord and the placenta do all the work to keep the baby healthy. Once the baby is born, their body has to immediately be responsible for all of its own functions. These sensations and processes feel quite weird to your baby at first, and they may make faces and sounds to express how they are feeling. 


During sleep, your baby’s brain is still hard at work. In the first part of your baby’s sleep, active/light sleep, your baby has increased blood flow to their brain. This is how your baby’s brain grows. There is a lot of activity happening in their brain during light sleep, and their body often reacts to this stimulation by moving, twitching, making lots of noises and facial expressions including smiles. We also believe that babies dream, and although there is no way to determine what they may be dreaming about, we’d like to think that those sweet smiles during their sleep are in response to dreams about drinking milk or snuggles with mom or dad. During the second half of your newborn’s sleep cycle, deep/quiet sleep, your baby’s brain is resting.  This is the time when your baby’s brain is storing memories. There is usually less movement, noises, and facial expressions during deep sleep. 

Beyond 3 months

Once your little one is around 3 months old, you may begin to notice many new skills. This is the time when your baby really begins to interact with you, follows your movements, and responds to your voice and face by mimicking you. This is also the time when you will begin to see smiles when your baby is awake and responding to you. These smiles are usually the ones that become predictable, because you consistently see how your baby smiles in response to seeing and hearing you. 

As you build your new relationship with your newborn, you and your baby will begin to develop your own form of communication. Those early smiles that you see during your baby’s sleep are tell-tale signs that their brains are growing rapidly and that their body is practicing all the movements it needs for development of muscles. Most parents will agree that every time they see their baby smile, during sleep or awake time, they fall in love even more with their little one.  Regardless of the reason for your baby’s smiles, they usually evoke such positive emotions in you that it causes you to smile and feel happy. Therefore, enjoy every smile that you see from your baby in those early weeks, and know that soon enough you will be able to witness even more smiles as a direct result of the interactions you share with your baby as they continue to develop and mature.

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