100% mineral filter sunscreens are formulated with zinc oxide and/or titanium dioxide. These actives are opaque powders, and work by creating a physical barrier on top of the skin to reflect and scatter UV rays. Therefore, a 100% mineral based sunscreen can leave an ashy, purple or white cast on some skin tones. To help the formula blend into the skin, work in small sections and apply in circular motions. Rub well until the formula is no longer visible.