When you brush your teeth, why does the toothpaste sometimes froth up, whereas other times it turns to a watery texture?

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When you brush your teeth, why does the toothpaste sometimes froth up, whereas other times it turns to a watery texture?

In: 6

Frothing is principally controlled by how much of the mixture is aerated. In some sense it’s like whisking. The more you whisk, the more foamy it gets. Also, the foaming is controlled by the surface tension of the liquid. That’s why foaming soap is easier than foaming oil (think mayonnaise).

This is determined by how viscous your saliva is, the chemistry of your saliva at that moment, the amount of water (dilution) of the liquids in your mouth. It’s like whisking pancake batter and cookie dough, essentially same but the amount of water determines how much foam it can have.

Finally, how much froth is also determined by the brushing action. Essentially, of the brushing action is able to push air inside the liquid, it froths more. Think on the lines of how whisking works again. If you whisk like a normal person, you get foam. Of you whisk like a maniac (think poking the batter with whisk) it doesn’t work that well.