Often newborns will smile in their sleep. Sometimes a smile in the early weeks of life is simply a sign that your little bundle is passing gas. But starting between 6 and 8 weeks of life, babies develop a "social smile" -- an intentional gesture of warmth meant just for you. This is an important milestone.

Can babies smile at 4 weeks old?

It may be possible for your baby to smile at 4 weeks but usually only while he's sleeping. This is called a reflex smile. Your little one may not flash a true smile until about 6 weeks or a little older, and these true smiles happen when he's awake and alert.

Do babies smile instinctively?

Newborns also smile in response to sweet tastes and smells. These findings were published decades ago when smiles were considered purely as innate reflexes. The reason that scientists at the time didn't interpret them as emotional was partly because the smiles looked different to social smiles.