Your lunch box's lid is the problem, not the box.

You can usually put the bottom of a lunch box in the dishwasher, but the lid is where the trouble starts. The container itself — whether it’s plastic, glass, or stainless steel — is typically fine. The lid is what gets betrayed.

Most lids have a silicone gasket or a plastic latch that can warp in the heat. After a dozen cycles, that seal loses its snugness, and suddenly your soup leaks all over your backpack. Dishwasher detergents are also harsher than you think; they can cloud clear plastic and make it look cloudy. If the label says top rack only, that warning is mostly for the lid.

Bento boxes that are one solid piece usually survive fine. But if your box has any wood, bamboo, or that cardboard-paper feel, keep it out. Also, don’t assume metal is safe — look for a lining. Aluminum boxes can discolor or corrode in the dishwasher.

When in doubt, hand wash the lid. It takes ten seconds, and you’ll keep that lunch box way longer.