We recommend that you only use Scholl Roller Heads with Scholl Velvet Smooth Electronic Foot Files and replace every 3 months for ideal efficacy. You can remove hard skin with this roller head on wet, soaked or dry feet. For use in/under water, use only with Scholl Velvet Smooth Rechargeable Waterproof Foot File. Retain the outer packaging for future reference. Refer to the packaging of your Scholl Velvet Smooth Electronic Foot File for full usage instructions.