Baking soda and sunlight fix most lunch-box smells.

Baking soda paste plus a few hours of direct sunlight will kill most stubborn lunch-box odors.

Dish soap only cleans the surface. Smells from curry, tomato sauce, or fish get trapped in the micro-scratches and pores of the plastic, and soap can’t reach in there.

The fix is a one-two punch. First, coat the inside with a thick paste of baking soda and a little water. Let it sit for a few hours — overnight is better. Rinse it out. Then put the box in direct sunlight for a couple of hours. The UV light actually breaks down the odor-causing molecules. You’ll be surprised how well this works.

White vinegar works as a backup — a soak of one part vinegar to three parts water for an hour, then a wash. It smells like vinegar for a bit, but that fades fast.

If it still smells after the baking soda and sun treatment, the plastic itself has degraded. Throw it out. You can scrub plastic for a week and it won’t come back.

Sun and baking soda are free — try them before you buy a new one. If they fail, the box has earned its retirement.