An overproduction of certain hormones causes skin cells to reproduce. Then, those cells block
off the oil glands. The blockage occurs within the middle layer of skin, so scrubbing your face
does not get deep enough to remove the blockage. When oil glands are first blocked, they
produce tiny white bumps called whiteheads or closed comedones. Bacteria may then grow in
the blocked oil glands and produce red bumps or even pus bumps. When the oil glands open
spontaneously, black color change is often noted, thereby called blackheads or open comedones