Baking soda fixes lunch box smell. Here's the routine.

Lunch boxes reek after washing because the smell is baked into the plastic itself, and the fix is a baking soda paste soak, not more soap.

Soap only removes surface gunk. Fish oil seeps into micro-scratches in plastic, and the dishwasher can actually make it worse — the heat sets the oil into the polymer. That’s why the box smells worse after a hot cycle than before.

The fix: mix baking soda with a little water into a thick paste, coat the inside, let it sit overnight, then wash normally. A white vinegar rinse works too. For really stubborn cases, leave the box open in direct sunlight for a day — UV kills the odor-causing bacteria. And dry it fully before putting the lid on. Moisture trapped inside is how the smell comes back even after you cleaned it.

One prevention tip: never store the box sealed shut when it’s empty. Give it airflow between uses. And if it’s a cheap plastic box that still stinks after all that, throw it out. The smell is in the polymer forever. Your next tuna sandwich doesn’t deserve that.