[putnambr]

Soaps that don't include detergents are safe for cast iron, too. Many people confuse carbon and crud buildup for 'seasoning'. The seasoning you want is a micrometer-scale carbonized oil on the surface of the steel, and possible some excess carbon buildup to fill in any surface pores. A mild soap won't affect this, at all.

You can definitely damage a pan leaving it wet, so of course make sure to heat it up on the stove after washing and drying to cook off any remnants of water. I'll usually put on a very thin layer of Crisco if I've used soap.

[Sunspark]

You mean soaps that don't include caustic lye. Just about every dish soap is a detergent and safe for use with cast iron as they are not caustic.