ELI5; why do reusable bottles and mugs need washing before use?

Question

ELI5; why do reusable bottles and mugs need washing before use?

In: Chemistry

Answer 1

If you mean before consumption after purchase, then you want to clean away any debris or bacteria as sanitization is not often part of the manufacturing process. Also, you never know what’s happened to a product between the factory and the store, the store and you.

Or LY5: it’s like finding a toy on the playground; let mommy clean it before you put it in your mouth.