8 Things You Should Never Put in the Dishwasher (And Why)
Meta Description: That shattered glass in the dishwasher is a nightmare scenario. Discover the 8 common household items you should never put in the dishwasher to avoid damage, ruin, and dangerous messes.
Introduction
The image above depicts a homeowner’s worst nightmare: a dishwasher cycle gone wrong, resulting in shattered glass scattered across the racks and the floor. While the text mentions the dishwasher “exploded,” the reality is likely that a fragile item succumbed to thermal shock (rapid temperature change) or the high-pressure water jets simply broke a weak piece of glass.
Dishwashers are marvels of modern convenience, but they are harsh environments. They use high heat, powerful water jets, and caustic detergents designed to strip away grease and food. Not everything can survive that treatment.
Here is a list of 8 common items you should never put in the dishwasher, and the science behind why they belong in the sink.
1. Cast Iron Skillets
The Why: Cast iron relies on a layer of polymerized oil called “seasoning” to create a non-stick surface and prevent rust. Dishwasher detergent is highly alkaline and abrasive. It will strip the seasoning right off the pan in a single cycle, leaving you with a bare, rust-prone metal skillet that will stick to everything you cook.
2. Wooden Cutting Boards and Utensils
The Why: Wood is porous and absorbent. The high heat and prolonged soaking in a dishwasher cause wood fibers to expand and contract rapidly. This leads to warping, cracking, and splitting. Once a wooden board cracks, it becomes a breeding ground for bacteria that is impossible to clean.
3. Sharp Chef’s Knives
The Why: There are two reasons to keep good knives out of the machine. First, the harsh detergent and the high-pressure water can dull the sharp edge over time. Second, and more dangerously, the violent movement inside the dishwasher can cause the knife to bang against other metal utensils, chipping the blade. Plus, reaching into a loaded dishwasher to grab a sharp knife is a recipe for a cut finger.
4. Non-Stick Cookware (Teflon)
The Why: Non-stick coatings are delicate. The abrasive detergents used in dishwashers act like sandpaper on the coating. Over time, the non-stick surface will peel, flake, and lose its effectiveness. Most manufacturers explicitly state that hand-washing is required to maintain the warranty.
5. Crystal and Delicate Glassware
The Why: This is the most likely culprit for the disaster in the image above.
Thermal Shock: If you put a cold glass dish into a dishwasher that immediately starts a hot wash cycle, the rapid expansion of the glass can cause it to shatter.
Etching: The high heat and harsh detergents can cause “etching” on crystal and fine glass, leaving it permanently cloudy and dull.
Vibration: The powerful jets can vibrate delicate stems (like wine glasses) until they snap or knock against other dishes and break.
6. Aluminum Pots and Pans
The Why: Aluminum is a reactive metal. The high heat and alkaline detergents in a dishwasher cause oxidation. This turns the aluminum a dull, dark gray or black color and can actually pit the surface of the metal. It can also leave a metallic residue on other dishes in the load.
The Why: Many plastic containers (like takeout containers or older Tupperware) cannot withstand the heat of the drying cycle. They can warp, melt, or release chemicals into the plastic. Even if they don’t melt, the heat can degrade the plastic over time, making it cloudy and harder to clean. Always look for the “Dishwasher Safe” symbol (usually a square with water droplets) on the bottom.
8. Insulated Travel Mugs (Yeti, Stanley, etc.)
The Why: High-end insulated mugs rely on a vacuum seal between two layers of steel to keep drinks hot or cold. The extreme heat of a dishwasher can damage the seal or the powder coating on the outside. Once the vacuum seal is compromised, the mug loses its ability to insulate, effectively turning it into a regular, single-walled cup.
Conclusion
While it is tempting to throw everything into the dishwasher to save time, doing so can ruin your favorite kitchen tools and create dangerous situations like the one shown in the photo. When in doubt, hand wash items made of wood, cast iron, sharp metal, or delicate glass. It takes a few extra minutes, but it will save your cookware—and your floor—from disaster.
