Applying eyelash extensions is a practice that enhances the length, thickness and fullness of natural lashes. The Lashes used consist of silk, mink, or synthetic hair. In this method the extensions are carefully placed one by one with minimal glue to avoid any clumping. Your eyelash extensions should last 3-4 weeks before needing a fill. To avoid premature loss of lash extensions, avoid using any cosmetic products, or makeup removers that contain oils.