A baby’s first smile is a fun milestone for parents. It means they are becoming more aware of their surroundings and are becoming social and expressive. Parents are often surprised when they discover that babies smile in their sleep. While experts don’t completely understand the phenomenon, it might be that a baby smiles in sleep while dreaming or in response to stimuli.

When Do Babies First Smile?

Many parents report that their babies have been smiling since their very first day. This isn’t exactly true. Babies smile in a primitive way in response to stimuli, often when passing gas and sometimes when hungry.

A baby doesn’t produce what people recognize as a social smile—an intentional facial expression—until six to eight weeks of age. Babies smile for the same reasons anyone does: to interact with people, express happiness, and get attention from others.

Why Do Newborns Smile in Their Sleep?

Babies smile while sleeping—an adorable habit parents love to catch. Why they do this is not fully understood, but there are some possible reasons:

• It’s a reflex. As with those early infancy smiles when your baby releases some gas, a sleep smile might be a reflexive action. It could be a result of passing gas or having a bowel movement. There is also some evidence from research that babies smile in response to pleasant stimuli, like the aroma of a food they like.
• They’re in active sleep. Babies, like adults, go through several sleep phases throughout the night. REM sleep in adults is known as active sleep in children. Why babies move more during this phase isn’t known, but it seems to trigger twitching, sucking, and smiling.
• Your baby is dreaming. Experts have yet to determine if babies dream, but if they do, a smile could arise during a pleasant one.
• They’re processing. Some experts hypothesize that babies smile, or even laugh, during sleep as they process daytime experiences. If true, the nighttime smile is simply an expression of emotional development.

Is a Baby Laughing in Sleep Normal?

Smiling is more common, but your baby might also laugh while sleeping. This won’t occur until they have developed the ability to laugh while awake. As with smiling, laughing might be a response to a dream or a way of processing and evolving emotions.

Laughing during sleep is generally normal and not a cause for concern. In extremely rare cases, it could be a sign of a type of seizure known as a gelastic seizure. Only about 1% of cases of epilepsy are gelastic. A gelastic seizure causes uncontrollable laughter and sometimes a grimace or smile. If you suspect your baby is having any type of seizure, get medical help immediately.

Every parent wants a happy, smiling baby. Regardless of the cause, a smile during sleep likely indicates that your baby is content. If you have difficulties getting your baby to sleep through the night, try soothing sounds like the ones available on BetterSleep. The baby-friendly sound mixes might just help your little one smile into sleep.