The first step in controlling any pest is not to put down some poison, but is to study and learn about 1) what conditions cause them to be present and 2) how to correct those conditions so they cannot breed. Silverfish need warm and moist places to live and grow so look for those types of places and eliminate them. Their food source is varied and includes anything with protein in it.

Here is a link that might be useful: Silverfish

I understand that they need moisture but if a bathroom is next to my closet wall, how is it possible to control it? You would think inside my room and drawers would be dry, wouldn't they?

They move from the warm and moist environment to other places in search of a food source. Not even a bathroom should be so warm and moist that it would create a good environmment for siverfish, or any other critter, to take up residence. If your bathroom stays that moist you have other problems that need to be addressed.

And bear in mind that they pose no hazard to your health.

While Silverfish may not pose a health hazard the conditions they need to live in can. Hot, moist areas can produce mold spores that adversly affect your respiratory system.