Is My Baby Smiling, or Does She Just Have Gas?

Dr. Jacobson says babies should start smiling between four weeks and two months so don't be fooled by earlier "grins."

At first you may notice smiles while they sleep, which is referred to as a "reflexive smile." The main difference is that it's not triggered by a social stimulation, according to the American Psychological Association. Or perhaps you've seen a "gas smile," which happens when they're passing wind.

It can be hard to tell the difference between social smiles and these other types, but one clue: typically, other smiles are characterized by an upturn of the lips. When they give you a social smile, they'll smile with their whole face.

A genuine or "social smile" represents friendliness and pleasure. It's a milestone because it shows the baby is smiling as a form of communication. Aw!

"Between four and six months of age, the baby is smiling, giggling, and very fun to have around," Dr. Jacobson says. And around five months you might be able to elicit a full belly laugh. But it's not uncommon if babies start laughing sooner or later than that.

And fair warning, it's not all giggles for everyone: "By six months of age, the baby also has good grasp, so they pull hair very well," Dr. Jacobson warns. Watch out!

Now the fun really begins! "At the one-year mark, the baby should be clapping, waving bye-bye, blowing kissing, giving hugs, and playing peekaboo," Dr. Jacobson says.

But remember: milestones are a reference point, not hard-and-fast rules. So try to avoid comparing your baby to their peers, and if you have a concern, stay off Dr. Google and run it by your actual doctor. "The best source of developmental milestones is your pediatrician," Dr. Jacobson says.