When in doubt, hand wash it

The dishwasher-safe symbol on the bottom of the lunch box is the only reliable way to know — and if that symbol has worn off, your safest move is to assume it isn’t.

The symbol looks like a little stack of plates with water squiggles above it, sometimes labeled “dishwasher safe.” Mirrors, plates, cups — same icon. But plastic lunch boxes get that embossed symbol worn smooth after a few months of scrubbing, so you can’t always count on it. That’s when the material matters more.

Polypropylene (the #5 recycle symbol) handles dishwasher heat fine. Most cheap food containers are made of it — those you can run through a cycle with confidence. Melamine and acrylic will warp or crazed. Stainless steel lunch boxes are trickier: the steel itself survives, but insulated ones rely on a vacuum seal that dishwashers can slowly wreck, and the rubber gaskets and lids will smell and lose their snap.

So, real talk: if it’s a classic bento-style plastic box and it says dishwasher safe, great. If it’s steel, insulated, or has a rubber seal and you can’t find the symbol — just hand wash it. A few minutes of scrubbing beats buying a replacement.