Occasionally a hamster's toenails may become overgrown. Dwarf Campbells Russians do have very long nails as they mature and this is usually nothing to worry about. However, if a hamster is scratching itself during washing due to long nails or the nails are starting to curl underneath the feet then they will need treatment.
Lining a box with sandpaper and letting the hamster run around in the box for a short while each evening will often file the nails down. (Sandpaper should not be used to line the floor of the cage.) However, in some cases it may be necessary file the nails down with a nail file or to clip them. If you attempt to do this yourself you will need someone else to hold the hamster while you file or clip the nails and you must be careful not to cut the nails down too much as you may cause the nails to bleed. Alternatively you can take the hamster to a vet to get the nails clipped.