What are the disadvantages of metal straws?

Metal straws are usually made from stainless steel, which is a resource-intensive material to produce.
Metal straws can cause bacterial infections if you do not clean them well.
The extraction process for metals uses fossil fuels that add to the growing global warming issue.

Can mold grow in metal straws?

Stainless steel metal straws are perfect vessels for mold and bacteria from food particles left behind—even after thorough rinsing. Metal straws mask what might be growing on the inside, and it's advised that metal straws be soaked and scrubbed with a long brush. Dishwashers aren't enough!