Blackheads are skin follicles, also known as open comedones. They are filled with sebum and dead cells. They have undergone certain chemical reaction, resulting in the oxidation of melanin, making the color to become black.
Whiteheads are skin follicles, also known as closed comedones. They are also filled with sebum and dead cells. But their skin surface has only microscopic openings. Since the air cannot reach the follicle, the material is not oxidized, thus remains white.
If blackheads or whiteheads are infected, use prescription topical antibiotics, or oral antibiotics. If comedones are not infected, antibiotics do not help.