If you store your donabe without drying it completely, or if it's left in the humid environment for days, the mold might grow in the donabe as it's earthenware. If you are worried about it to happen, we suggest you check your donabe sometimes to make sure it's very dry and no mold is growing inside. Please see our How To Take Care of Your Donabe page for the tip to remove any moldy smell from the donabe. The stain might stay, but after it's treated, it's safe to use again.