Why Do Babies Smile in Their Sleep?

Reasons Babies Smile in Their Sleep

Until more research is done, it is difficult to say for sure why infants smile during sleep. So far, evidence is conflicting, and the reasons for smiling during sleep may change depending on the baby’s age and what stage of sleep Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source they are in. 

Rapid Eye Movement (REM) or Active Sleep

The vast majority of newborns’ smiles during sleep appear to occur when the eyes are moving rapidly, as they would during a dream. Studies suggest that adults smile in response to positive dream imagery Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source , but it is difficult to say whether this is also true in babies. 

The sleep cycle for newborns comprises three stages of sleep: quiet sleep, indeterminate sleep, and active sleep. Active sleep is similar to the rapid eye movement (REM) sleep stage seen in adults, when people typically dream Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source . During REM sleep, brain waves speed up, the eyes move rapidly beneath closed eyelids, and most muscles are temporarily paralyzed, so the person does not move while dreaming. 

One major difference between active sleep and adult REM sleep is that infants are not paralyzed during active sleep. While in active sleep, an infant may twitch, make sucking motions, move their limbs, smile, or frown. Researchers have observed that newborns sometimes make faces with complex expressions Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source during REM sleep, even before showing these same expressions while awake. As a result, a baby’s first smile may occur during sleep. 

Older research has described infant smiles during sleep as reflex-like. Studies suggest that smiles during active sleep are generated in the cerebral cortex, the outer part of the brain. Researchers believe spontaneous smiles that occur during sleep may help develop the muscles used to smile Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source and lay the groundwork for smiling and laughter as the child grows. 

Can a Baby’s Smile or Laugh Be a Cause for Concern?    

Less commonly, a baby may laugh due to a gelastic seizure Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source . Gelastic seizures are an extremely rare type of seizure that causes a person to laugh uncontrollably Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source , but generally without the amusement that usually accompanies laughter. One-third of people who have these types of seizures experience their first one as an infant .

Infants may experience a gelastic seizure when they are on the brink of falling asleep. If a gelastic seizure occurs during sleep, a baby may wake up and then go back to sleep when the seizure is over. Gelastic seizures tend to last just 10 or 20 seconds and may occur along with other symptoms, such as squirming, grunting, or lip smacking.

Caregivers who notice concerning symptoms in their child or infant should talk to their pediatrician, who can help them find a specialist if needed.

When Babies Start to Smile 

Babies may smile soon after birth. However, a newborn’s smile is usually a reflexive response to an internal physical feeling, such as gas or hunger. This is in contrast to an adult’s smile, which communicates pleasure Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source . Experts cannot say for sure whether a newborn baby’s smile conveys any meaning about their emotions. 

In general, a newborn baby’s facial expressions may not represent the same emotions that similar facial expressions would in an adult. For example, sometimes newborn babies appear to be laughing when they are actually unhappy, or they may raise their cheek muscles as a reflex to someone touching them. Even in older infants up to 1 year of age, smiles do not necessarily mean the infant is happy.

Babies do not produce their first full smile until they are approximately 2 months old. This type of smile is called a social smile because the baby uses it to interact with their caregivers. Social smiles develop around the same time as other emotional facial expressions Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source . 

Once they learn to smile, babies can better communicate with adults. At first, babies may produce a social smile without looking directly at a person, but this is normal. They should start building up stamina for holding people’s gazes over time. 

When a newborn smiles during REM sleep, most experts consider the smile to be spontaneous rather than a social smile. These spontaneous smiles usually feature a closed mouth. By contrast, when a baby starts to perform social smiles while awake, these smiles are done with an open mouth, which is seen as more genuine. That said, some studies have observed social-type smiles in babies during active sleep.

How to Encourage a Baby to Smile

Taking actions that show the baby they are loved may help coax out their first smiles. That said, although babies hit a number of milestones — including smiling — throughout their first year of life, not all babies reach these milestones at the same time Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source . 

A baby’s smile is an important social tool that helps them communicate positive emotions and bond with their caregiver. Babies notice when their caregivers are paying attention to them, and a smile may be their response. Primary caregivers and siblings may receive more smiles, while extended family and friends may need to wait until the baby warms up to them first.

Smiling back when a baby smiles and taking care of their needs can help them feel secure and confident, and it helps lay the ground for social skills Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source later in life. Babies can also detect when their caregivers are not happy. Research has found that babies smile and laugh less when their caregivers are depressed or anxious. 

Some ways to encourage a baby to smile include:

• Making funny faces or sticking out your tongue
• Smiling at the baby
• Singing or talking in a high-pitched voice
• Tickling the baby 

More broadly, smiling in babies often appears to relate to sleep. Research suggests that smiley infants who bond with parents at bedtime may also sleep better Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source because they have a stronger sense of trust and security. 

Bedtime routines that help caregivers bond with an infant include singing lullabies, feeding, or cuddling. Interacting with an infant while they are actually asleep does not appear to make them smile more.

Not all babies start smiling at the same time. However, if your baby is not smiling by the age of 3 months, if they have skipped other milestones, or if you notice any other concerning symptoms, it is a good idea to mention this to your pediatrician.