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Ever wonder why babies drool and put everything in their mouths?

Carlin Webster, 8 months, demonstrates drooling, which starts at 3 months.
Carlin Webster, 8 months, demonstrates drooling, which starts at 3 months.
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Friday, February 25, 2011; 3:24 PM

Ever wondered why babies drool and put everything in their mouths?

I'm guessing that most of the kids reading this have little brothers and sisters or baby cousins. If so, this article will explain why drool stains are all over your home and your parents' clothes. For the rest of you, spend some time watching babies the next time you go to the park so you can see what you're missing.

Saliva is an important part of our digestive system. It moistens food to make it easier to swallow and begins to digest starches before they get to your stomach.

There are hundreds of tiny salivary glands in your mouth that are designed to keep it moist. These glands are functioning at birth. But the big boys, the ones that turn on when you eat or chew, do not mature until a baby is about 3 months of age. (The large salivary glands are called the parotid glands.)

There are two other reasons why babies start to drool three months after birth. First, babies can finally bring their hands to their mouths intentionally. (Before this age, their hand movements were pretty clumsy.) Second, babies have developed the ability to chew, which stimulates the production of saliva.

Alas, the poor immature human has not yet learned how to control his oral secretions. Because saliva obeys the laws of gravity, it dribbles down the baby's chin and lands on anything or anyone unlucky enough to be in the area.

The above description explains how a baby gets his hands in his mouth and ends up drooling, but not why. The "why" is really cool.

If I blindfolded you and asked you to identify an object without looking at it, what part of your body would you use? The answer is your hand. You would pick up the object and move it around in your fingers until you figured out it was a key or an eraser or whatever it was that I had put in front of you. The reason for this is that you have more sensory (feeling) nerves and brain space devoted to your fingers than anywhere else on your body.

The same is not true for babies. A baby's most highly developed sensory area is in his mouth. So when a baby (or toddler) sticks an object in his mouth, it is not just to chew it. He is also feeling the object and exploring it with the sensory nerves that line his tongue and lips. (This is the same reason animals sniff everything in sight. They identify a large part of their world through smell.)

Bonus fact: Babies are not the only mammals that chew and drool. Man's best friend has similar habits. For some reason, this is more common with big dogs than little ones. That's why the 1989 movie "Turner and Hooch" and the never-ending series of "Beethoven" movies (1992 to 2008) featured big, slobbering dogs instead of cute little dogs. The little ones may yap a lot, but at least they don't drool!

- Howard Bennett

Howard Bennett, a Washington pediatrician, is the author of "Lions Aren't Scared of Shots."


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