Dishwasher Safe but Not Microwave Safe: Understanding the Science Behind Heat Resistance in Dishware

Many of us have wondered why some dishware is labeled as dishwasher safe but not microwave safe. It seems counterintuitive, as dishwashers often reach higher temperatures than microwaves. However, the science behind heat resistance in dishware reveals that it’s not just about the temperature, but also about the way these appliances heat the dishes. Let’s delve into the fascinating world of heat resistance in dishware to understand why this is the case.

Understanding Heat Resistance in Dishware

Heat resistance in dishware is determined by the materials used in its construction and their ability to withstand different types of heat. Dishwashers and microwaves heat dishes in fundamentally different ways, which is why a dish can be safe for one but not the other.

Dishwasher Heat

Dishwashers heat dishes by spraying hot water and steam, which heats the dishes evenly from all sides. The heat is also gradual, allowing the dish to expand slowly and evenly, reducing the risk of cracking or breaking. Most dishes, including those made of glass, ceramic, and certain types of plastic, can withstand this type of heat.

Microwave Heat

Microwaves, on the other hand, heat dishes by emitting microwaves that excite the water molecules in the food. This process can cause uneven heating, with some parts of the dish getting much hotter than others. This uneven heating can cause thermal stress, leading to cracking or breaking in dishes not designed to withstand it.

Why Some Dishes Are Not Microwave Safe

Some materials used in dishware, such as certain types of plastic, can’t withstand the high, uneven heat generated by microwaves. They may warp, melt, or even release harmful chemicals when microwaved. Metal dishes or dishes with metallic paint or trim can also cause sparks or fires when microwaved.

Why Some Dishes Are Dishwasher Safe But Not Microwave Safe

Dishes labeled as dishwasher safe but not microwave safe are typically made of materials that can withstand the even, gradual heat of a dishwasher but not the high, uneven heat of a microwave. These dishes may also have metallic paint or trim that can withstand a dishwasher’s water-based heat but can cause sparks or fires in a microwave.


Understanding the science behind heat resistance in dishware can help us use our dishes safely and effectively. Always check the manufacturer’s instructions before using a dish in the dishwasher or microwave, and when in doubt, opt for hand washing and avoid microwaving.