The Serious Reason Why Some Food Containers Are Only Top-Rack Dishwasher Safe

It’s the end of a bustling day in the kitchen and a daunting pile of dishes from meal prep, afternoon snacks, and that ambitious baking project you started is staring you down from across the kitchen. As you roll up your sleeves to dive in and load every plate, platter, and container into the trusty dishwasher, there’s probably a pause when you get to your reusable food containers—where am I supposed to put this?

This is an important question to ask, especially when it comes to reusable food containers made out of plastic. Where you put them in the dishwasher, or whether you decide to load them at all, can affect the quality and usability of your containers—you don’t want your favorite carrier of chicken shawarma bowls to turn into a slightly wonky piece of plastic. But it’s also a matter of your health, as some plastics may leach dangerous chemicals when loaded incorrectly into the dishwasher.

Related: 10 Things You Should Never Put in the Dishwasher

Here we’ll explain why certain food containers are only top-rack dishwasher safe—so you can keep your reusable food containers intact and safe to use.

How your dishwasher works

To understand why plastic containers are off-limits to certain parts of your dishwasher, let’s first understand how your dishwasher works.

When you’ve added the last handful of silverware and closed the door of your dishwasher, it begins the cycle by filling the basin of the machine with water. The heating element at the bottom of the machine then heats up the water. After soap gets added, a pump propels the hot, soapy water through the spray arms to spin around for about 30 minutes. After the dishes are rinsed, the same heating element turns on again to dry the dishes.

Related: Is There Actually a “Best” Way to Load the Dishwasher?

The aforementioned heating element reaches temperatures ranging from 105°F to 155°F—hot enough to melt certain plastics, including those that make up your food containers (typically polypropylene). If you load reusable plastic food containers on the bottom rack, they’re closer to the heating element and at higher risk of melting. By loading them on the top rack, you lower the risk of damaged containers.

Why melted food containers can be dangerous for your health

In addition to causing misshapen containers, melted plastic also poses a potential risk for your health. The high heat can cause harmful chemicals to leach out from the plastic containers. The most notable of these is Bisphenol A, or BPA, which has been linked to health issues including cardiovascular disease and an increased risk of breast and prostate cancers.

Most food containers are no longer made with BPA, though it is only officially FDA-banned in baby bottles, sippy cups, and infant formula packaging. Be particularly careful with older pieces, takeout containers and anything with the resin code “7” as they may still contain BPA.

Related: The Setting on Your Dishwasher That's Killing Your Machine

Even on containers marked BPA- and phthalates-free, it’s still smart to be wary about potential chemical leaching. The BPA replacements still pose concerns for chemical leaching, with some studies showing evidence that they still leach out estrogen-like chemicals.

To combat this potential chemical leaching, avoid exposing your reusable containers to the high heat of the dishwasher by loading them on the top rack of the dishwasher. Place them there securely so no pieces fall to the bottom and melt (and get stuck in the machine). Additionally, avoid choosing dishwasher cycles such as “sanitize” that use higher temperatures if you’re running a load with reusable plastic containers.

And remember, if all else fails... there's always good old-fashioned handwashing!