Acne is caused when a hair follicle get clogged with an oil called sebum and skin cells.
Skin bacteria thrive and multiply in sebum, causing inflammation. Some acne consists of
simple blackheads and whiteheads. Inflammation within the pore causes a pimple (also
called a “papule”) or a pus-filled pimple (“pustule”), depending on how deep it is. If it’s
really deep, it can cause a painful cyst -- and scarring.