This oily substance, called sebum, is one of the main causes of acne. Although it is essential to keep our skin soft and pliable and our hair shiny, too much of it can be a problem. Especially in teenagers, large levels of a sex hormone, called testosterone, are produced, which causes the skin to release a lot of sebum, too. Sometimes, this excess sebum can clog up the pores.
Adding to the mix are dead skin cells. About 30,000 skin cells are shed every minute! A lot of these skin cells are shed inside the pores themselves.
A blocked skin pore also contains bacteria. They feed off the dead skin cells and the clogged sebum within the pores and produce toxins that damage the lining of the pores. As these bacteria grow and multiply, they invade the area surrounding the pore, which can lead to a bacterial infection.
A blocked pore initially turns red because blood rushes to the site, which is one of the ways our body responds to an infection. Then, white blood cells—a type of blood cell responsible for fighting infection—destroy bacteria, build up below the surface of the skin, and die.
These dead white blood cells, along with dead skin cells and some bacteria, form a white liquid known as pus. A pimple forms when the excess sebum and dead skin cells clog up and block the opening of the pore. This type of pimple is called a whitehead (Fig. 2a).
Another type of pimple, called a blackhead (Fig. 2b), appears when sebum and dead skin cells clog the pore but not the opening, as in a whitehead. While the pore is clogged, its surface remains open. A blackhead appears black because melanin in the dead skin cells reacts with oxygen from the air, which changes the melanin’s color from brown to black.
Two types of pimples: (a) a whitehead; and (b) a blackhead (respectively)