If you keep the Garnier Pure Charcoal Black Serum Mask (28 g) on for more than 15 minutes, it will not give extra benefits because your skin usually absorbs the serum within the recommended time; instead, the sheet may start to dry out and pull moisture back from your skin, which can cause dryness, tightness, or irritation, especially for sensitive skin, so it is best to remove it after 15 minutes and gently massage in the remaining serum.

Usually, applying a sheet mask once a week provides a balanced boost of hydration and glow; however, the right frequency depends on your skin type, condition, and overall routine, as some may benefit from more regular use while others with sensitive or well‑maintained skin may prefer less, so it’s best to pay attention to how your skin responds and avoid overuse to prevent irritation or sensitivity.