Eyelash extension primer is a product used by lash artists before applying eyelash extensions to natural lashes. Its main purpose is to cleanse and prepare the natural lashes, removing oils, dirt, and makeup residue that could prevent the lash adhesive from bonding properly. By creating a clean surface, the primer helps to ensure a stronger, longer-lasting bond between the natural lash and the extension. It can also help improve the overall retention of the extensions, resulting in less shedding and better wear over time.