Be sure your hands are clean while working on greenware. Any kind of hand cream may cause stains or hard spots on fired ware.
Mold that appears in moist clay is not only harmless, it's beneficial. Mold will improve the clay's plasticity, making it easier to work with. Some people even introduce organic matter such as old rotting leaves into their clay to promote the growth of mold.
Grog is fired clay which has been crushed and screened. It is used with slip or modeling clay to achieve textured effects and will reduce warping and cracking in hand modeled ware.
A small amount of bleach added to slip, glaze or recycled clay mixtures eliminate mold which may occur and cause smelling. The bleach may be caustic on your hands so you may want to wear gloves when handling. Though this mould introduces plasticity to your clay.