Baking soda fixes the fish smell, but the wash is the real fix

Your lunch box smells like last week’s fish because fish oils are still in the plastic, and a quick rinse isn’t touching that.

Fish smell is oil, not water. Soap and hot water break it down, but you have to actually scrub the whole thing — lid, corners, seams — not just swish it. If you did that and it still stinks, make a paste of baking soda and water, coat the inside, and let it sit overnight. Rinse it out with vinegar the next morning. Sunlight also kills odors, so leave it open in the sun for a few hours if you can.

If it still smells after that, the plastic has absorbed the oil permanently and it’s done. That box is never coming back. Toss it and don’t eat out of it.

Going forward, don’t put fish in the box loose. Use a sealed glass container inside the box, and wash the box the same day you bring it home. “Tomorrow” is where fish smell goes to breed.