At puberty large amounts of hormones throughout the body cause the oil glands to make more oil. Usually you notice that your skin is more oily before the acne appears. The oil and cells that line the pores can stick together and cause a plug to form in the pore. The result is a blackhead, if the pore is open, or a whitehead, if the pore is closed. The blackhead is not dirt, so scrubbing and lots of washing won't make it go away.
Whiteheads are the beginnings of pimples, or zits.
When the oil in the closed pore breaks through, the skin is irritated from underneath, creating a pimple. If you scrub, pinch, or rub your face too much, you may cause the pores to break, causing even more irritation and more pimples. Pinching and popping pimples, whiteheads, and blackheads usually causes more problems, and sometimes scarring. Foods like chocolate, sweets, french fries, etc. almost never make acne worse. Some makeup, cover-up or hair styling aids may block pores, so be careful about what you use.