The secret is scrubbing seams, not just rinsing.

To properly sanitize a lunch box, wash it with hot soapy water, scrub every crevice with a small brush, and then dry it completely before closing.

Most lunch box mold isn’t from the main compartment — it’s from food sludge hiding in the hinge, the edges, or under a rubber seal. Hot water and dish soap alone won’t reach those. Use a bottle brush, a toothbrush, or a cotton swab and actually dig into the grooves. If it’s dishwasher-safe, that helps, but it still won’t guarantee the corners get blasted.

For a deeper sanitize, use a food-safe dilute bleach solution: about one tablespoon of unscented bleach per gallon of water. Let it sit for a couple minutes in the crevices, then rinse thoroughly and air dry. On fabric or insulated bags, check the label — most are machine washable, and if not, wipe down with soapy water and a vinegar solution, then leave open to dry.

The drying step is non-negotiable. Mold needs moisture, so never close the bag until it’s fully dry inside and out. Do that and the nasty smells never get a chance to start.