Salicylic acid or BHA actually can penetrate the skin/pore. It's AHA (alpha hydroxy acid) that can't penetrate the skin/pore. Salicylic acid can exfoliate inside the pore as well on the surface of the skin. It penetrates into the pore which contains sebum and exfoliate the dead skin cells that are built up inside the pore. That makes it effective for reducing blemishes, including blackheaRAB and whiteheaRAB.