Acne is a skin condition that causes whiteheads, blackheads, and inflamed red growths (papules, pustules, and cysts) to form. These growths are commonly called pimples or "zits". It occurs when tiny holes on the surface of the skin, called pores, become clogged. Each pore is an opening to a follicle, which contains a hair and an oil gland. These oil glands help lubricate the skin and help remove old skin cells.
When glands produce too much oil, the pores can become blocked. Dirt, debris, bacteria, and inflammatory cells build up. The blockage is called a plug or comedone.
The top of the plug may be white (whitehead) or dark (blackhead). If the plug breaks open, the material inside causes swelling and red bumps to form. If the inflammation is deep in your skin, the pimples may enlarge to form firm, painful cysts.
Acne IS a problem of swelling and inflammation, NOT a problem caused by bacteria.