Mold hides under the silicone gasket.

The best way to prevent mold in a lunch box is to take the silicone seal out and wash it separately every single time.

Mold grows where water and food particles hide. That little groove around the lid is exactly that place, and the seal covers it. If you only rinse the lid or toss it in the dishwasher, the area under the gasket stays damp and dirty. Dishwashers also blast silicone around and can warp it over time, which ruins the seal.

So after use, pop the ring out, wash the lid and the ring with hot soapy water, and dry them both completely before putting it back together. I like to wipe the groove with a paper towel or a small brush. Once a week, give the ring a soak in white vinegar or a little diluted bleach just to kill any spores that might be starting.

Just get in the habit of pulling the seal out. It’s a ten-second step that makes a huge difference.

Future You won’t be gagging on that sour smell at lunch.