Except
for long-haired hamsters, they do not require grooming
by a human. Hamsters groom themselves on a regular basis.
Long-haired hamsters require brushing only to remove
shavings and other items that will get stuck in their
fur.
Some recommend that you have a dish of sand for
the hamster to roll in. This will help them remove some of the
natural oils from the coat and avoid them from becoming too
greasy. It can actually adversly affect a hamster to bathe it.
That will remove most of the natural oils that their fur has.