That's why the first time I brought out the dish soap to wash one of my cast iron pans, my grandmother wailed with disapproval. I assured her I knew the history—older dish soaps were made with lye, which would strip seasoning and even damage pans—but it is perfectly fine to wash cast iron with soap these days.
In short, yes, it is safe to wash cast iron cookware with mild dish soap or castile soap. However, avoid strong degreasing soaps and detergents to prevent damaging your pan's seasoning layer. Scrub lightly with a dish brush, rinse and dry well, and apply a thin coat of oil to the pan after washing.
While soap will not hurt your cast-iron pan, water will, because it will cause the metal to rust, and so that is the thing you should not use on a cast-iron pan.
Putting your cast iron pan in the dishwasher will cause it to rust. Dishwasher detergent can strip the seasoning, exposing the pan's interior to water and oxygen, and the prolonged soaking will give the entire surface plenty of time to oxidize. The hot water in the dishwasher will speed up the rust formation process.
Cooks for generations didn't use soap on cast iron pans because the soaps were made with lye and vinegar, two ingredients that will absolutely strip seasoning and can even damange the pan's iron. Today's aerosol oven cleaners are often made with lye, or sodium hydroxide.
CLEAN CAST-IRON SKILLET AFTER EVERY USE
Rinse under hot running water, scrubbing with nonmetal brush or nonabrasive scrub pad to remove any traces of food. (Use small amount of soap if you like; rinse well.) Need to remove stubborn stuck-on food and grime? See our more intensive cleaning tips for tackling them.
Non-stick, cast iron, and aluminum pots and pans should never go into the dishwasher. Non-stick coating will wear out in the dishwasher, cast iron will rust and lose its seasoning, and aluminum will be covered in nicks and scratches.
If cast iron is left in the sink to soak, put in the dishwasher, or allowed to air dry, it will rust. It can also happen when you store your cookware in moisture-prone environments, such as a cabinet near a dishwasher, an open cabinet in a humid location, or stored outside.
Cast iron cookware rusts easily when exposed to moisture - this is why it is so important to dry your cast iron thoroughly after each use. The prolonged exposure to water in a dishwasher is too much for cast iron. The heat dry setting doesn't do a fantastic job either; it tends to leave a ton of moisture behind.
There's no need to throw away a cast iron skillet that's a little (or a lot) rusty. In fact, the next time you stumble upon some rusty pots and pans at an antique store or flea market, imagine the potential!
► Lead to Rust Formation
Oxidation is a common consequence of using dish soap to wash cars. Oxidation is rust, and it forms due to a combination of sunlight, moisture, and oxygen exposure. When automotive wax and paint are jeopardized or in poor condition, dish soap applications can quickly lead to rust formation.
After you've used your skillet, use a sponge to scrub it with water. But don't let it soak in water, as this can cause rusting. If it still needs a bit more attention, add some kosher salt to the pan and scrub with a damp sponge. The salt acts an abrasive cleaner without disturbing the seasoning.
But you don't need soap.
Many cast iron purists simply wipe their pan clean after cooking instead of exposing the pan to water and harsh scrub brushes. But for those of us who'd prefer a cleaner cast iron skillet, oil and kosher salt are more effective than soap and a sponge will ever be.
You can use olive oil to season cast iron, but you need to choose a high quality extra virgin olive oil, which should have a smoke point close to 400 degrees Fahrenheit.
Although salt is hard, it's still softer than cast iron, so it doesn't risk scratching the surface of your skillet.
Cast iron pans can leach a sizeable amount of iron into your food, exceeding dietary intake in some cases. Acidic foods will contribute to much more leaching while an old, heavily-seasoned pan will leach much less iron than a newer one.
If a crack appears in your cast iron pan, it's time to ditch it. Even a hairline crack will expand and contract when heated and cooled, and ultimately the pan will split—a potentially dangerous situation if it happens during cooking! Plus, cracks are difficult to clean and may harbor bacteria and rust.
Can cast iron cause iron toxicity? Only people with hemochromatosis are at risk of iron toxicity from cast iron cookware. Even then, the risk is low, since a new, well-seasoned cast iron pan only leaches about five milligrams of iron per cup of food.
Food and moisture will deteriorate the seasoned surface and cause it to rust. Never put cast iron pans in the dishwasher or let them soak in a sink of water. Never put cold liquid into a very hot cast iron pan. The pan could easily crack or warp.
Dry thoroughly right after you clean—do not let your cast iron air dry. Set on the stove over medium heat to evaporate any remaining water. Rub with a thin coat of vegetable oil (about a ½ teaspoon for a 10 inch skillet) until evenly coated and shiny. Let cool completely and store in a dry place.
For general cleaning, do not use copper scrubbers or steel wool as these can be too abrasive and will remove seasoning. Instead, opt for chainmail scrubbers, pan scrapers or cast iron scrub brushes which will be gentler on your pan's seasoning.
lovely to look at, but still dirty. What's going on? Editor: It sounds to me like you might be cleaning a bit to rigorously and are removing the baked-on seasoning. If you're scraping down old cast iron to re-season from scratch, then it sounds like you've done enough and are ready to start re-seasoning.
Cast Iron Skillet Cleaning Method: Salt and Paper Towel
The method: Pour 1 cup coarse kosher salt into the still-warm skillet. Use a folded kitchen towel to scour. Discard the salt and rinse the skillet with hot water.