As previously discussed, acne is caused by three things: (1) the P. acnes bacteria, (2) sebum and (3) dead skin cells (or dirt, etc.). Skin cells are produced deep in the basal (base) layer of the epidermis and rise towards the surface over time, die and are sloughed off. Note that sebum production is controlled by many, many factors (hormones, diet, genetics, etc.) which is part of the reason why it can be so difficult to figure out the "cause" of anyone's acne.
Excess sebum/dead skin/dirt
What is ACNE?
Acne is the result of the sebum (oily substance produced by the skin's oil glands), P. acnes bacteria (which occurs naturally and lives off of sebum), and dead skin cells or dirt, etc. that get trapped in your pores.
Overproduction of sebum and/or dead skin cells result in those things getting trapped by forrming a "plug" in your folicles, which causes the bacteria to flourish = infammation = acne. In properly functioning skin, the sebum should help to carry out dead skin cel