The lid is the only thing you need to hand-wash.

You can usually put a lunch box in the dishwasher, but the lid is the part you should wash by hand.

The body of most lunch boxes is fine. Plastic ones are dishwasher-safe as long as they’re marked (check the bottom) and you put them on the top rack. Stainless steel containers are fine too. Silicone is basically indestructible in there.

The trouble is always the lid. Those rubber gaskets warp in heat, and the little locking tabs get brittle. You’ll end up with a lid that doesn’t seal, and then your soup leaks everywhere. Also, warm soapy water is fine, but the high heat of a sanitize cycle will eventually make cheap plastic turn cloudy.

So do the 15-second hand-wash on the lid, and you’ll be fine. Your future self will thank you when the seal still clicks.