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

Before first use, you mean? Because in the manufacturing process the machine lubricants and people handling them before they’re packaged etc can still be on the surfaces of the item, and are not meant for consumption, even if they’re usually harmless. So it’s better to wash it to clean it properly.