But actually, the damage is far more likely to occur because of exposure to water. Yup, water — not soap — will destroy your prized cast-iron cookware.
That’s not to say that you shouldn’t use water at all! You should. But, once the pan has been cleaned of bits of food and grease, the best and most important thing you can do for the health and good looks of your cast iron is to dry it off immediately. Cast-iron pans, even the most artistically seasoned ones, will develop rust at an alarmingly fast rate.