It all begins when your oil glands make too much oil. This excess oil mixes with other substances (such as dead skin) in the pore, causing a clog. Not surprisingly, this clog makes it difficult for the oil to flow freely, which causes the pore itself to enlarge. Even though the pore enlarges to provide extra room for the oil to flow out, the oil still can become trapped (especially around the nose) by dead skin. Once this occurs and the oil and dead skin at the end of the clogged pore is exposed to the air, it oxidizes, forming a blackhead. Yuck! Dr. Corey Hartman emphasizes that “oil production and pore size are largely genetically determined”.