Busted: Blackheads are merely whiteheads that have undergone the process of oxidation. (So no, blackheads aren’t dirt!)
Oxidation is merely a chemical reaction happening in your skin. Think of what happens to an apple when you cut it open and it darkens: this is oxidation.
When the follicle (pore) opens up, oxygen enters, causing the oil and dead skin cells within the follicle to undergo oxidation. This leads to the dark color you see.
Whiteheads are follicles that are filled with the same material, but have only a microscopic opening to the skin surface. Since the air cannot reach the follicle, the material is not oxidized, and remains white.