Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
8. Chemistry in the World
What makes an acid not good?
There are several ways to interpret the question, and so there are several answers. That makes it more fun.
It is not good to get acid in your eye. It hurts. The acid changes the shape of the proteins in your eye and skin, so those proteins don’t work the way they normally do. Your body responds to this by sending pain signals to your brain, so you stop putting acid in your eye.
In your stomach, acid is produced by your body to help you digest your food and to kill microorganisms that might make you sick. It changes the protein called pepsin into the right shape to help break down the proteins in your food. Stomach acid also helps break the food down into smaller pieces, so it can be absorbed in your intestines.