Reusable Containers
Storage containers purchased specifically for keeping fresh food or leftovers in refrigerators and freezers and those made for repeated use such as baby bottles are typically safe to put into dishwashers. Labels often indicate whether the items are microwave and dishwasher safe, and some indicate whether the containers are safe for washing only in the top rack of the appliance. Lightweight disposable containers commonly start to warp and crack after a few washings, even if they are confined to the top rack
Grocery Store and Take-out Containers
Containers in which yogurt, cream cheese, whipped toppings or microwave meals are sold are typically not dishwasher safe and break down under intense heat and harsh detergents. Placing them in the top rack of the dishwasher during the first cleaning is a good way to determine their durability. Many hard plastic take-out containers appear sturdy and reusable but they often emit harmful chemicals when exposed to high temperatures and should never be reused.
Types of Plastic
Non-disposable plastic containers and tableware are generally made from styrene, acrylic, acrylic blends, melamine, polypropylene or polycarbonate. Styrene and acrylic are safe to wash in the top dishwasher rack although this washing method will cause them to prematurely cloud and develop fine cracks. Blends of styrene and acrylic are more durable and can be washed in the bottom rack, as can melamine, polypropylene and polycarbonate.
Dishwasher Guidelines
Even if your plastic containers are made of materials deemed safe for bottom rack dishwasher cleaning, use the top rack if possible as newer, higher-end dishwashers often reach extremely high temperatures that exceed commercial testing standards. If your dishwasher has a low or delicate cycle, plastic containers are often safe in both top and bottom racks. Always secure plastic containers with metal or ceramic dishes placed next to them to prevent them from dislodging during dishwasher cycles and ending up in the bottom of machine. Fallen containers can melt or catch fire if they land on heating elements or prevent the dishwasher water from properly draining.