2. Localized skin inflammation as a result of over activity of the oil glands at the base of hair follicles: Acne appears when oil (sebaceous) glands come to life around puberty when these glands are stimulated by male hormones that are produced in the adrenal glands of both boys and girls.
The oil glands, which are located just beneath the skin, continuously produce and secrete oil through openings in the skin. The oil lubricates and protects the skin.
Under certain circumstances, cells that are close to the openings of the oil glands block the openings. This causes a buildup of oil underneath the skin.
Certain bacteria feast on this oil, multiply, and cause the surrounding tissues to become inflamed.
If the inflammation is near the surface, a person will get a pustule. If it's deeper, it is called a papule (pimple). And if still deeper, it is termed a cyst.
If the oil breaks though to the surface, the result is a "whitehead". If the oil becomes oxidized (that is, acted on by oxygen in the air), the oil changes from white to black, and the result is a "blackhead".