Why does the mask need to dry completely before removal, and how do you know when it is ready?

The drying phase is an active part of how the formula works, not simply a waiting period. As the mask dries over approximately ten minutes, the kaolin clay and zinc oxide are drawing out impurities, absorbing excess sebum, and allowing the salicylic acid and papain to work against the dead cell layer. You will know the mask is fully dry when it visibly hardens and begins to crack across the surface. Removing it before this point cuts the exfoliation process short and reduces effectiveness. Once fully dry, the mask should be removed by massaging in gentle circular motions using a warm, damp cloth or dry fingertips, which activates a final mild physical exfoliation as the dried mask material lifts away. This two-stage process, active drying followed by massage removal, is what gives the Light Skin Peel its characteristic revitalizing effect on the complexion.