Dishwasher the containers. Hand-wash the bag.

Your lunch box itself should never go in the dishwasher, but the containers inside are usually fine with some common sense.

The lunch box — the actual bag or hard-sided shell — stays out. The heat and water destroy the insulation, soften the shell, and wreck zippers and latches. Even the hard plastic ones warp after a few cycles. Hand-wash that thing.

The containers are a different story. Glass and silicone are fine. Most plastic food containers — look for the #5 polypropylene triangle — are fine on the top rack. The weak spot is the lids. The rubber gasket that makes a leak-proof seal doesn’t love high heat. Run it through enough hot cycles and it degrades, and suddenly your soup is swimming in your bag.

The real killer is the heated dry cycle. That’s when the heat spikes and warps lids. Use normal wash with heated dry off, or just pull the lids out and air-dry them on the counter. If a container doesn’t have the little dishwasher-safe symbol (a glass with water droplets), don’t risk it.

The ten seconds it takes to hand-wash a lid beats buying a new container every two months.